Depends if you're nubguard spec. The sac abilities are nice if you have that talent.

But as far as using the succy for reliable crowd control, I wouldn't. Might ask if Xzin's having better luck with his, I know he has a post about a succubus cc macro, so he is doing it.

If you have no other option though, it's better than nothing. Fear is a no go for the most part, depending how you're pulling. If you're pulling mobs far back once you have the room to do so, Fear is probably the best CC you have, it holds a long time, and for warlocks at least, I barely ever break it with shadowbolts.

An imp is going to be a better option as a pet than a succ, imo, for blood pact and dark pact if you spec that way (dark pact ftw). Then you're left with a lot of other better choices as well for the other lock's pet.

I'd say it'd be situational, if you feel you need the succubus it can be there, but I personally don't use it unless I have to.