Mistakes happen and not having to waste a brez after a mistake is worthwhile. We all like to think we don't make mistakes but we do especially on progression. The other thing is cheat doesn't just save you from your own mistakes, it can save you from other people's mistakes or things that aren't really mistakes at all. If a healer is slow on a terrorize dispel or a shaman is slow on a tremor drop cheat can save you. If you a healer falls behind on healing and you get "triaged" cheat can save you. Does cheat save me every pull? Nope but compared to the other options on that tier for general purpose survivability cheat is very strong. You can make a good case for leeching poison as combat, as assassination the healing isn't good enough to justify the choice.Anyway Cheat Death is fine for these kind of mechanics or mechanics where you are forced to soak something special like Zon'ozz's orb in Dragon Soul. Other than that I really don't get why people spec into Cheat Death unless they aren't that good at avoiding things and this actually gives them a lot more DPS from not dying as often.
On Topic: Power Word: Smoke bomb is really powerful, one of and possibly the most powerful melee dps raid cd in the game.