OK it IS possible, but if you have common sense and some guidance (this forum, watch the AG videos a few times) and are semi-careful, it would be nearly impossible to put buffer trails into the paint. Just make sure you use the right amount of product, and don't put TOO much pressure on the machine.
If you wanted to put some buffer trails in the paint, you might be able to. However, if you're a beginner learning this machine, you have little to worry about. I just bought a UDM and tried it out for the first time a couple weeks ago. I'm a beginner, so I'm pretty slow with the machine, but I have absolutely no fear that I'm going to damage the paint using OP and an Orange LC Pad (currently my most aggressive combo).
So start out slow. If you're really scared of damaging your paint, try the machine out on a friend's old car that wouldn't mind. (they should be thanking you, actually). Or, go get a painted body panel thats in good shape at the junkyard. Or, just go at it on your own car and remember to take it slow, one step at a time.
Good luck!