Affliction’s strengths in raids are mostly multi-target, especially 3 or more targets, and it’s mobility is insane compared to Destro or demo, and most specs in the game. It is a spec that thrives on fights with adds that can give you high stacks of wrath of consumption and sometimes reap stacks.
Some examples of the fights affliction is very good on are: Renferal, the spiders although infrequent provide you with some minor WoC uptime, and the fight has a large amount of moving around. Odyn, While affliction is not that great at runebearer damage, if your guild needs it that is; BUT you get WoC stacks from them, and that’s enough to get it close to Destro in phase 1 / 2 cleave. It’s got straight up better ST and better mobility for phase 3.
Cenarius. SO MUCH MOVEMENT AAAAAARRRRGH!!
But Affliction’s most important strength is Absolute Corruption cheesing. Especially on Dragons / Helya are excellent examples of fights for affliction to shine, also AC lets you ungodly damage to dragons and tentacles (keep in mind this is not padding), as both fights have adds that you can maintain 5 stacks of WoC from for large parts of the fight, both fights have a decent amount of movement. And just about every fight you play Destro on aff is competitive with it (it’s not always better, in fact it’s worse more often than not; but it’s close enough that it’s never going to hurt your raid). Demo is 100% required if you want to be a warlock on any ST fight though.