Of course, sleep is good. It regenerates, rejuvenates, restores, etc. But I think it's possible that too much sleep on the weekends can be a bad thing, esp. when you have to wake up before 6 a.m. every weekday. If you're sleeping past noon on the weekends, and then trying to throw everything back into balance for a totally different schedule during the week, it's wreaking havoc on the internal clock. I used to have a terrible habit of doing this at my old duty station, and it was so hard for me to fall asleep on Sunday nights that I sometimes barely slept at all.
Just a quick, practical tip for readers -- if possible, don't throw your personal schedule way out of balance on the weekends or days off.