Affliction is a harder spec to play. If you make even a few mistakes, your DPS will suffer.
That said, it is also very rewarding. Drain life affliction is extremely effective at keeping you alive, your healers happy, and your raid progressing. I will never use any other spec on fights like Chimaeron, Nefarian, Twilight Council... it's just a very useful spec when every fight has a lot of damage going out and your healers need all the help they can get.
You really shouldn't give, as evidence, a fight where you're supposed to control your DPS and not go all out.