I originally began this as a thread on the Paizo Publishing message boards in a discussion about the tactical considerations of "blasting" versus alternatives when playing classes like wizards and sorcerers in Pathfinder (or D&D 1st edition, 2nd edition, and 3rd edition). Someone asked if it was true that "blasting" was less effective in D&D/Pathfinder than other alternatives.
"Blasting" is essentially damage dealing spells. These are the spells most commonly recognized in D&D/Pathfinder, such as magic missile and fireball, and are most commonly chosen by those new to the game. "Alternatives" is pretty much magic that doesn't revolve around dealing damage (at least not directly), such as haste, silent image, or enlarge person.
Blasting has lost a lot of spark since it's previous editions. I love 3rd Edition D&D / Pathfinder, but stuff like fireball was better back in 1st edition and 2nd edition because enemies had less hit points. You could be fighting monstrous demons who only had around 40-60 hit points, whereas the Pit Fiend and Balor have over 300 hit points each in the current edition. The thing is, damage hasn't really increased much. Fireball still deals the same 10d6 fire damage at 10th level (average 35 damage), but that can't even down a Bear outright unless you roll about 80% of your max damage, and it still gets a Saving Throw for half damage.
The second problem that blasting has is it's very limited. Most damaging spells don't have secondary effects or special features for using them, with the exception of fireball (which notes that it can catch unattended flammable objects on fire) most things just deal damage, and even fireball's secondary effects aren't terribly useful (actually, they make it riskier to use since you might accidentally start a forest fire or something). This means that unless you're actively attacking an enemy, the spell is useless to you, and only useful on the round you actually cast it (not before, not after, only during).
The third problem is that most damaging spells are incredibly situational. Things like energy resistance are pretty common in D&D/Pathfinder. For example, any simple fiendish creature has at least fire and cold resistance 5 (but up to 15), meaning they ignore that much damage when they're hit with those elements. Let's use a hypothetical Wolf with the Fiendish creature template, which we could find summoned by a summon monster spell, or serving some evil villain as a minion. At 5th level, our wizard inflicts 5d6 (average 17.5) fire damage with a fireball spell, or half damage (about 8.75) on a successful save, and then reduces the damage by 5; meaning the fireball probably isn't going to kill the 13 Hp wolf outright; but you can only do this maybe 1-2 more times today. Likewise, if you find yourself fighting a Fire Elemental of any size, your fireball is completely useless.
And for those wondering, a 5th level Ranger should have about a +8 to hit (+5 base attack, +4 strength, +1 masterwork weapon, -2 power attack) and deals around 2d6+12 damage, killing the wolf outright on a successful hit. So the 5th level ranger can kill one or two of these things per round without expending precious resources like 3rd level spells.
So What Besides Blasting?
There's a lot of better things that a wizard or sorcerer can be doing instead of trying to compete with the fighting guys at dealing damage. If a wizard or sorcerer really wants to do well and be important in a fight, it's better to change the conditions of that fight. There's a lot of ways to do this. A successful wizard can do this in a variety of very noticeable ways.
1) Buffing: A wizard can act as a "force multiplier", making his friends far more powerful than they normally would be. Casters can do this as early as 1st level, and they make it count. A 1st level wizard can cast enlarge person on the party's fighting guy, making him bigger, badder, and beefier, and it lasts 10 rounds (1 minute). That means the wizard can turn the fighter into an engine of destruction, and then either cast more spells or stall his turns by just defending (total defense gives a +4 dodge bonus for 1 round as a standard action) to increase his own survivability. He can also cast protection from evil on the fighter, preventing the fighter from getting mind-controlled and turning on the party.
At 3rd level, the wizard can cast spells like heroism to give the fighter a +2 to most everything for 30 minutes (and enlarge person lasts 30 rounds now), or cast bull's strength on the fighter making him hit harder, or casting invisibility on the party's rogue so she can sneak into an area to scout and steal the badguys' potions and scrolls before they fight them.
At 5th level, the wizard turns into a true force multiplier. He can cast spells like haste which can affect the whole party, making them faster, more accurate, harder to hit, better at evading, and even lets them get an extra attack in. Since it lasts 5 rounds, you just made everyone on your side much better for most or maybe even all of the fight.
It goes on with more and more options as your levels rise. New spells to make your party stronger become available, and old spells become more plentiful and last longer and longer; so spells that you used to cast only when you needed them can be cast beforehand and last for a good while, so you can prepare for trouble (sorry, cheesy reference).
2) Debuffing: A wizard can also make it easier for enemies to get mashed by the party's fighters. This is a bit harder than making your friends stronger, but it too can be done as early as 1st level and right on up to 20th. Spells like sleep and colorspray can knock enemies out, while grease can make enemies slip, slide, and fall down (making them easier to hit), or can even force an opponent to drop their weapon.
At 3rd level, a wizard gets stuff like hideous laughter which can take an enemy out of a fight. Glitterdust can blind a group of enemies for a few rounds (usually enough to mop them up) while outlining them so they can't hide. Blindness/Deafness can make them permanently blind until they get magical assistance. Web can trap enemies in sticky nets of webbing, making it difficult to move or fight, and other things like this.
At 5th level, a wizard can cast spells like stinking cloud, slow, and ray of exhaustion, which pretty much disable enemies (often groups of enemies) for several rounds or an entire combat, allowing the party to mop them up; and the wizard can conserve his spells.
3) Controlling: The third in the holy trinity of wizard casting is controlling the field. Controlling essentially means that you make the battlefield or conditions favor your party on a more broad scale than just buffing your party. This can involve summoning monsters to help your party with spells like summon monster I-IX, or making certain areas of the field hazardous for your enemies with spells like grease and stinking cloud. In many cases, controlling has a lot of spells that overlap as debuff spells.
At 1st level, controlling spells include things like grease to make areas of terrain troublesome. Sleep can help take enemies out of the fight for a few rounds, giving you and your friends some breathing room. Silent image or obscuring mist can conjure hazy clouds of smoke or mist that provide concealment, potentially robbing enemy rogues of their ability to get bonus damage against you or your party.
There are a lot of great controlling spells, but I'm going to point out just a few of my favorites. Sleet storm is a 3rd level spell that is amazing at controlling the battlefield, as it blocks all sight and covers a very noticeable area in rough terrain for a number of rounds. Black tentacles is a 4th level spell that creates a big area that grabs enemies and beats them up while stopping them from acting. Stinking Cloud is a 3rd level spell that can block sight and make enemies nauseated, which prevents them from acting.
Then of course there are the summoning spells. Summoning spells are a special kind of battlefield control because they literally place new creatures on the battlefield. When suddenly you have a fiendish bull bursting onto the scene, clogging up the path to your friends with its body and getting ready to trample over your enemies, you're doing good. Either they have to kill the bull (wasting their turns) or they have to try and kill the party while the bull tramples them; it's a win/win deal.
Summary: Ultimately the reason that damaging spells aren't very useful is because they lack options and they're here and gone. If you enlarge your fighter, he'll be kicking booty for a while. But you could also enlarge him to help him carry stuff, or to help him climb something, or to reach something, or to make it so something cannot pin him down, or so he cannot be caught in a web or net. You have options. All you can do with magic missile is damage creatures, and only damage creatures.
We can experience a thousand and one different situations while playing a D&D/Pathfinder campaign, so it's generally better to be prepared. Being able to conserve your spells, help you party, and adapt to different situations is what separates a good wizard from a wand of fireball.