I never understood this. You keep all your music in iTunes. What harm could possibly come even if it did accidentally wipe your device? The worst possible scenario is that you'll have to wait a few minutes to sync it back again.
Not an iTunes user, but I guess some people just want to do a selective sync to certain devices to keep storage use in check and maintain library navigability on the device. That can be quite a bit of work which you wouldn't want to lose to technical failure.
The "correct" way to do this is to make a playlist of the things you want on your device, and then to tell iTunes to sync to that playlist (or collection of playlists) only.
Then I spend the next half hour looking at the connected device to ensure my collection is still there.
It's part of the reason why I switched over to the (defunct) Rdio. Managing the individual iTunes music files was just too stressful.