I'll do that if the music quality is irritating, and I get the sudden inspiration to look for better. I would never do it because, for instance, hey, only 64kbps. If it is listenable, it is listenable, and I don't even consider the file format.
Irritating could be a bad vinyl rip (eg from one of my own scratched LPs!) as often as it is a symptom of low bit rates.
disclosure: My relative-to-many-others fairly-small digital music library is mostly of an arbitrary standard that says, lossless FLAC wherever possible, and 320- or 180-MP3 where not. The reason I say arbitrary, is that I have never taken the trouble to find out, by listening tests, at what point I, personally, really can hear the difference.
I do keep lossy copies for portable use, in another location. Probably nothing over 180-MP3.