I don't understand Arcane in dungeons

[:1]So they pull the boss, I start casting Arcane Blast ... and I just continue casting it until the boss dies because I don't see a reason to use anything else?

Well, that's not entirely true ... I usually put up Mirror Images and then use AP and then a little later use a gem for the dps boost ... is there something else I'm supposed to be doing ?
In normal dungens, bosses die within the span of 1 burn cycle, so thats really all you should be doing.
In heroic dungens, I'd guess they die in about 1-3 burn cycles, so it'd be there you perfect your rotation and mana management.
I won't pretend to even be able to guess how many cycles it takes to down raid bosses.
But the entire point of my post is how there's no rotation because casting the same spell over and over is #1

Even if I wanted to cast Barrage to drop my stack for mana reasons, why would I cast Missiles?
Thats the point Thirdegree was making.

In Normals spamming just Arcane Blast with your cooldowns and using a mana gem is correct because the normal boss health is just that low.

In Heroics and Raids however, the bosses have much higher health values, meaning instead of just doing the burn phase (Which is what your doing in normals) you will also have to use your conservation phase. Meaning the core part of the spec is based around a longer period of time than just normal instances. Theres always fire if you want a rotation, but Arcane is majorly overpowered in normals.

Thats the point Thirdegree was making.

In Normals spamming just Arcane Blast with your cooldowns and using a mana gem is correct because the normal boss health is just that low.

In Heroics and Raids however, the bosses have much higher health values, meaning instead of just doing the burn phase (Which is what your doing in normals) you will also have to use your conservation phase. Meaning the core part of the spec is based around a longer period of time than just normal instances. Theres always fire if you want a rotation, but Arcane is majorly overpowered in normals.

I really should have explained that better :/
In 5mans bosses have like 4mil hp give or take, you really don't have try at all.
In 10man raids bosses have 30+ mil, that's when managing your mana gets a bit tricky.
Yeah in normals that's what it's like mostly. The point is managing cd timing, as well as the mana through burn and conserve phases because of mastery. During movement fights you will also need to be doing a bit more pre planning because of how centered your dps is on keeping AB stacks up. Arcane certainly does have a rotation, and can be incredible dps, but also very unforgiving of small mistakes. Not sure what lvl the arc mage is you are using, but also knowing boss mechanics etc.. for when to pop cd's. If you are a lower lvl before master of have the right gear it might be worth it to wait to pop cd's and take some dmg with mana shield and stack some incanters absorption. Also I would suggest a macro that uses improved mana gem and POM at the same time since you can spec into POM to make it give the next 2 spells +15% chance to crit. And your improved mana gem will boost your dps through mastery as well as a raw sp boost. Just wait for 4 stacks obv.