Well technically it's still illegal, but typically Game Boy games don't have official soundtracks you can buy so there's no harm in sharing them. SPC sets, especially for popular games like FF VI or Chrono Trigger, are more of a gray area, but I'm guessing the worst that could happen would be a cease & desist. In the case of PSF/PSF2/USF sets, you run into bandwidth and space issues on top of the fact that the list of ripped games is much less complete and that a lot of the ones that are ripped have commercial soundtracks.