I'm not sure, but perfect pitch MIGHT help in sight-reading.
I'm what you might call an 'extreme sight reader' - I play all sorts of stuff at sight, under pressure and without wishing to boast (because it's a freak ability, I don't really claim credit for it!) I often surprise myself. I make use of it playing for auditions and exams, but I've also sight-read the odd time in concerts and once in a live radio broadcast. I've always been very good at it, but it's clear to me that however good one's initial level, practice always helps.Perfect pitch certainly helps, as someone suggested, because one can more easily hear every note before putting a chord down, enabling one to do a 'sanity check' a few milliseconds ahead of actually playing. All the extreme sight readers I've met in my life (offhand I can think of 5 or 6) have perfect pitch.But there's no correlation, interestingly, between artistic attainment and sight reading ability. For instance, few would deny that Radu Lupu and Martha Argerich are two of the finest pianists around, but while the latter sight reads extremely fluently, the former is painfully slow. And one of the best sight readers of my generation, a guy I know quite well, doesn't perform professionally at all because he's really boring as a player (and knows he is). He's very busy, though, mostly as a repetiteur in contemporary opera because he can play the wierdest stuff, off a full orchestral score if need be.
Also, I get irritated by scores in which no thought is given to the practicality of page-turns. I am going to 'name and shame' ABRSM Publishing in this respect re their instrumental grade exam books (as opposed to their piano solo exam books in which they sometimes insert blank sheets to create easy page turns). Anyone who has had to accompany, say Richard Rodney Bennett's 'Buskin' from the current Grade 5 violin exam book piano part (especially unseen at an audition) will be with me in this! I have to maintain a collection of photocopies for difficult page turns in their books.