You're not supposed to - but most of us do it. In theory, you're only suppose to rest your wrists downwards when not typing, because doing so takes them out a neutral position. I'm not saying you should change, just trying to discourage the notion that's a healthy habit. (http://www.webmd.com/back-pain/proper-sitting-posture-for-ty...)

The specific model is relevant here as Apple laptops have a much deeper palm rest area than tiger machines.

I rest the bottom of my palms & the edge of my wrist. Maybe you're wearing your watch too loose and its sliding down your arm? My watch generally doesn't touch the top of the MBP 15" surface as i type.

I rest my wrists on my laptop whenever I'm not typing. But I type using 4 of my fingers though, lol.