Vocal tuning is something that in my opinion as a mixing and mastering engineer should be done before it reaches me. I'm often asked if I can tune vocals which I can do, but I always tell the client that vocal tuning is a creative process that is subjective to the person tuning the vocals. Vocal tuning should be done either in the production stage or once production has been completed and you are finalising the stems for mixing. I recently saw a poll on facebook which interacted with other engineers and producers from around the world, all of which seemed to have a similar opinion. In the image below you will see a screenshot of the poll and the amount of votes each category received.
As you can see topping the list is "engineer who is editing before mix engineer". Which also got my vote. Whilst there are quite a few joke categories in this poll it does put into perspective just how strong this opinion is. In an ideal world the vocalist will sing 100% in tune. Wishful thinking but most vocalists even the best vocalist need some slight tuning.