It's a very well-known fact (meaning, it's been supported by a lot of scientific research) that resting your wrists on anything while typing is not healthy because it compresses the small bones in your wrists (the carpal bones) which, in turn compress the nerves. It also forces you to use your fingers more when typing (instead of your whole arm, swinging) and puts you at risk for tendonitis in the in the hands, which is what happened to me.
This is not a matter of what is ergonomic for one person is not for another. It's a matter of physiology and body mechanics. You may be fine resting wrists on the palmrest for a long time, even forever, or it may cause damage. some people are more sensitive than others, but why take the risk? I can tell you from personal experience that it is not worth it.
In any case, Apple obviously was only concerned with beauty when they designed the MBP and macbook, not genuine ergonomics. There are more ergonomic laptops out there if you look at case design, trackpad button design, display height and tilt, for example.
