I find Discipline very useful for a lot of encounters, whether it be BoT BwD FL or even DS. Atonement healing is a big help, trust me... when you have archangel in your build and you're stacking your smite and holy fire damage (for more healing power) in a sense is somewhat like an AoE.
If every player is stacked in lets say a Magmaw fight or perhaps even Nef, your smite heal always goes to lowest health player that's closest, meaning if you spam it, it will heal whoever has the lowest health, right? But a big helping part of atonement healing is that archangel restores 5% of total mana when used and has a 30 second cooldown. That's a 10% per minute regain of total mana as well as your heals of every spell being increased by 15%.
Keeping your shield up is important too, assuming you won't be specced into strength and soul, you can't keep a constant uptime on shields for main tank, smites reduce the cooldown on your penance if specced properly so it helps a lot.
As far as AoE healing goes, it is a bit of a challenge but we help a lot (we can shield low health targets while the raid healer gets them all up in time for the next blow), we can also use prayer of mending with our 15% healing buff which is quite nice. Discipline obviously won't be as AoE efficient as Holy, but it is quite useful in my opinion, to have a disc priest in the group.