My first thought was 'What a waste of time', but on seconds thoughts it's not that bad an idea.
Now every guitarist should be able to look after his or her gear, but if you're playing a gig I can see how a guitar could go slightly out of tune between the time it was set up and when it actually gets played, or if you've put on a new set of strings that haven't quite settled in yet. In a live situation I can see how this would be great to have.
I went to see Muse at Wembly this year (yes it was great) and I saw the number of guitars that were wheeled on stage before they started. It wouldn't surprise me that after half an hour under stage lighting that the tuning might shift a little on 1 or 2 of those, especially the ones that weren't used until the end of a 2 hour set.