I'll add that the human ear is not as good at detecting deviation as is technology.

Here's a challenge to anybody who has Melodyne:

Take a vocal track you think is pretty good. Export it to Melodyne, and compare your sung notes to the grid. I think even a good singer will be surprised to visually confront the difference between the note they sang and the note they THOUGHT they sang.

What's more enlightening is that the deviations go in both directions.. some flat, some sharp.

Whether or not you choose to correct anything is still a personal choice. But it can be enlightening to see what you're really asking the listener to accept.

https://www.dropbox.com/sh/ey71h8ep047758h/AAC12jNM0Hz9Q8zsh5iDeqNHa?dl=0