Hmm... I have no inside information, but the way I guess skidmarks work is that each is saved on its own. So if two skidmarks are partially overlapping but weren't made at the same time, they wouldn't be saved as one large skidmark but still as two of them. Therefore, if tens of skidmarks were on the top of each others, each would still have to be drawn on its own. And soon or later LFS would use all of your machine's resources drawing skidmarks whose most wouldn't even be visible because they'd be hidden under others.