Reply to Mastering bootlegs/mashups?

This is a simple question... should bootlegs/mashups be mastered? If it's best to master a mashup, does anyone have any tips on mastering a bootleg with just added vocals to a track? and also would it be a different technique if it was a beat over another beat? I know mastering isn't basic stuff, but I avoid it because of it and I'm sure I shouldn't.