IMO, this is the only valid use of level matching; making a mix tape from other non-leveled files. By using leveling, you are actually introducing compression into the files that have to be leveled up (their peaks are now clipped because there doesn't exist a level above all bits on in the digital realm.
e,g, If you want to level your entire collection so it all has the same average volume.
1. You own a very hot album (like something by Rob Zombie) with limited dynamic range)
2. you own a very dynamic album with a much lower average level, but enough headroom to retain the juicy 15dB peak to average ratio of its drum rim shots.
If you run the whole collection into a level matcher, when the algorithm raises the average volume of the jazz album, it has to throw away some of the dynamic range, because the peaks can't go above all bits on