But it isn't the engineer who should control intonation! That is not the
engineer's job. ("It is now," I hear you say.)

No one is perfect. As I mentioned in another reply... sometimes a vocalist
hits a word with a certain character that cannot be easily reproduced... and
sometimes he/she is a hair flat are sharp doing so. I say go for the best
performance first... and if the singer was slightly off on a couple pitches
in that best performance... don't be afraid to nudge them. The same is true
for a solo guitarist... You might land that once in a lifetime guitar solo,
but discover that one bend didn't quite reach the target note. Don't throw
the solo away... make the subtle change that allows it to be used.

-S