When should you change stance?

Reading recent posts about Arms warriors, I have become interested in the issue of changing stance.

I am main spec prot with an arms spec I very rarely use (only for one tank boss fights where I draw the short straw). Is there ever a reason to change stance or switch to a 2H while still prot spec'd?

When I am arms on one tank boss fight and the tank dies, should I switch to defensive stance, and/or equip a sword and shield?

Sometimes I see feral cats going bear to save the raid and sometimes I see dps warriors having to step in when the tank dies, but I am not sure if the warriors are picking up a shield and/or changing stance.

Thanks for any advice!

A prot warrior will switch out of defensive stance to use one of the following abilities:
- Shattering throw
- Colossus Smash
- Hamstring
- Execute
Everything else you need is available in defensive stance. You might however also choose to switch to battle or zerker stance in 2 tank fights when you aren't tanking, to ensure that you don't pull threat back off the other tank. Personally, I tend not to use zerker stance because of the increased damage taken (which isn't significant, but neither is the bonus damage I get from zerker in the grand scheme of things). Beware, you can receive critical hits if you are out of defensive stance, so you use those abilities when you are not being hit.

As for arms warriors, there are a few answers. Arms can sometimes eek out more DPS by weaving in zerker stance. It's an advanced thing, if you aren't serious about arms then probably don't worry about it. The other thing is the scenario you describe where a dps warrior steps in to take over from the tank. It's certainly worth having a macro which equips a 1h+shield, possibly also popping shield wall, that you can press to 'save the day', and if you were doing that you'd do it in defensive stance. You might use the same macro to mitigate bursts in raid damage, but in that case it's up to you to decide if you'll also switch stance. You can also mitigate some raid damage just be switching into defensive stance (e.g. for a spike like crackle at nef) but that's a DPS loss, so you'd only do it situationally.

I have z, x and c on my keyboard as my stances, with macros that mean 'press once for stance, press again for action commonly associated with that stance'. e.g. press z for def stance, press z again to taunt.

stance dancing isn't all that necessary anymore. Blizz made enough changes that basically stance dancing is dead.

stance dancing give a warrior extra damage, doing more dps isn't dead.

Stance dancing for threat is dead gone and has a nicely engraved tombstone. But when your 2 tanking a fight and you stay in def stance even when your not tanking is just bad practice.

I stance dance constantly when playing arms. If I'm fighting a big group and tank has good threat, I will occasionally pop into berserk to do whirlwind. You can also assist by pummeling your opponent when opponent is casting, and switch to defensive to disarm opponent. The switching to defense is indeed a dps loss, so do it only if you want to support, but pummel and whirlwind away if you want to :).

I actually miss stance dancing as prot. Shockwave enemies, switch to battle, retaliation, switch to defense was such a nice aggro tanking to do against a group of mobs. Unless you want to whirlwind a group of mobs (they have to be shockwaved or otherwise massive stunned), I don't recommend stance dancing as prot

Quite frankly i find it the only way to not steal aggro backon a taunt swap fight short of pressing Esc.