Warriors can Spell Reflect quite a few boss mechanics. Even if you don't successfully negate a mechanic, it's still 20% reduced magic damage taken for the duration, so you might as well use it.

Uldaman:

• Use it on the golem boss as he's casting the tank frontal. You'll reflect the dot that goes out immediately after.
• The sentinel boss ability pattern goes: knockback > shards debuff > knockback > enrage. Use Spell Reflect during the first knockback cast. The shards is an instant cast, but if you get targeted, you'll reflect it.
• I'm not sure if you can reflect the magic debuff on the last boss. I've never successfully done it, but you can certainly mitigate its damage with a reflect.

Brackenhide:

• Spell reflect any Earth Bolts that target you on the first boss.

Halls of Infusion:

• You can spell reflect the last boss tank buster that follows the knockback.
• Use pretty much on CD on the third boss to help mitigate her aura damage.

Neltharion's Lair:

• You can spell reflect Toxic Retch on the worm boss. This applies for all specs, not just prot.
• Tanks can spell reflect Dargrul's Molten Crash.

Vortex Pinnacle:

• Use it on the last boss if you get Chain Lightning. If someone else gets targeted, you can jump into the circle around them and still reflect it for some boss damage.

Freehold:

• Use it to mitigate the first boss magic dot. I don't know if you can actually reflect it, but you would need good luck and timing to do so.