Yep, absolutely necessary for how I prefer to work.
For me the end justifies the means. The listener isn't going to give half a damn about how proud the talent was about how they recorded the take, and in most cases they'd never know anyway since it's not usually disclosed how a track was recorded. All people care about is if they like it or don't like it.
The way I see it is we can do a whole day of take after take after take to get things perfect and possibly losing the vibe and likely wearing the talent out, or we can get a killer performance and touch up the bits that are a bit rough. Pitch and timing can be easily adjusted, vibe and intensity can not. So long as that's in the bag and we have a great core performance, why put yourself and your talent through unnecessary work? As I said, no one else will likely know or care.
The other thing is backing vocals. For the silly amount of vocal layering I do, getting everything locked in super tight, especially dealing with a lot of different vocalists of various ability is a must. I like those big wall of vocal harmony parts and if a couple of the guys are off... argh, man it grates on me!
So yeah, absolutely - pitch correction software is a must in my studio.