Alchemy is a great (and possibly the best) DPS profession because of one thing: versatility.
Alchemy offers opportunities to tailor your DPS output on the fly, fight to fight, even phase to phase, that no other profession can compete with, for example:
You’re fighting the Northrend Beasts, you blew your cooldowns on Gormokk right from the jump, Rapid Fire, Call of the Wild, all popped immediately as your trinkets got their first proc off. You know Heroism/Bloodlust is going to go off when the worms come out, and you’ll pop your RF and CotW again when Icehowl smashes his face into the wall in phase 3, yes? Alchemy shines here, while you’ve downed a Flask of Endless Rage, which gives you (because of your Mixology talent) 244 attack power for 2 hours, you also have options:
There are at LEAST 4 potions that may prove useful for this fight: Wild Magic, Potion of Speed, Runic Healing and Runic Mana (real quick, what’s an anagram for potions? OPTIONS! Thank you, yes, I’m here all week). But possibly none are more valuable than the Crazy Alchemist’s Potion (which, of course, is only available to an alchemist). Say you’re running low on mana and/or health in this fight, pop one of these babies, and you get the base 3100-3500 health and 4200-4400 mana, but it can also proc, doubling either of the first two effects, or giving you Speed, Wild Magic, or one of a few assorted OTHER buffs, as well. Of course, if your health and mana are fine, you can also pop a potion of Speed or Wild Magic to assure yourself of the buffs, secure in the knowledge that popping that potion cost you less than someone with a (lesser) profession.
Want more versatility? Okay, instead of popping a flask of endless rage, how about elixirs of agility and intellect? Using the spreadsheet on femaledwarf.com, you can see that (mana dependent), it can be a DPS BOOST (by possibly keeping you out of Viper entirely) to use these instead of a flask of endless rage. Obviously these are available to anyone, but again, no other non-alchemist is going to be able to create them as cheaply as you can, and mixology is not a talent to be underestimated, as it will buff these elixirs, as well.
If you’re of the PvP bent, Alchemy shines here as well. Flask of the North (another alchemist only item) provides 80AP, 40 STR or 47 Spell Power, depending on what’s best for your class, and it works in arenas! It lasts for an hour, and has no cooldown, so you can refresh it whenever you like. While not as convenient as a perpetual buff like the extra sockets from BS, it’s a nice addition to a profession already packed with bonuses, and again, the utility offered incomparable, but let’s make a quick comparison anyway:
Alchemy vs. Jewelcrafting (my other profession), fight to fight versatility:
Okay, you’re a Jewelcrafter, gratz, and you need extra hit for a boss since the only Draenei in your raid is DC’d and had to be replaced (tell me this never happens, more spacegoats, please!). What can you do? Well, you can cut yourself a couple of replacement gems super fast, pop them in the best possible sockets, and off you go. But what happened here? You’ve replaced a gem or two with hit rating gems, and when you raid next time, you’ll have your spacegoat back, and want agility gems back in those spots. Cost effective? Hardly. How would an alchemist handle this sitch-e-ation? Pop a hit elixir and keep on truckin’. What? Raid wiped and the Draenei is back? You don’t need that crappy hit anymore, hooray! Pop another flask of endless rage and commence to crush the hopes and dreams of that boss, fo sho. Is this an extreme example? Sure. Is it a possibilty? Absolutely.
(I’m not going to get into the pros and cons of being hit capped in this article, but stay tuned, gentle reader, I may get around to it eventually!).
Pre-potting is another way to make use of the economy alchemy offers. Pre-potting, is, in short, quaffing a potion right before a pull, allowing you to get most of the buff of the first potion, and still allowing you the flexibility of drinking the appropriate potion later in the fight.
I hope I’ve convinced you to immediately switch to Alchemy instead of whichever lesser profession you favored prior to this little bolt of enlightenment, err article (or at least, failing that, given you a slight appreciation for it).