Big THX mate, I'd never have figured that out myself!!!
It was very important for me to know how this works, cause I'm not a fan of automatical unwrapping at all. I admit auto mapping has become very good lately, but no matter what 3D app, they just don't know wether I'm unwrapping just an apple or a human head. In most tutorials I watched, even professional ones the authors were using auto unwrap for heads and then fighting down the stretching piece by piece, which took them endlessly. I prefer making the seams myself and get a clean unwrap immediately.