"We'll fix it in post-production" can be a common sentiment at recording sessions. While there is a lot of technology for the audio engineer to use to improve a recording, some things just can't be fixed. An uninspired performance that is technically precise, in tone and in time, will be much more difficult to mix into a great track than a passionate performance with a few off notes mixed in. Know the limits of your engineer, and do what you can to help any musicians get into a state of mind that will accurately portray their passion for music.
You can read the full article here: http://therecordingrevolution.com/2012/12/03/one-thing-plugins-cant-fix/