For each file - yes. I've rarely seen an MP3 file compress at all. But across thousands of files, you start seeing some space economies
I did this right now at home, got 3% off on 1000 files - that's actually a lot less than I expected, as mp3 compression itself will interpolate some different (but similar to the ear) sounds into the same sound, which would then lend itself well to compression via reference...
Maybe if I had more pop music in my sample, it would compress better, as all pop music is pretty much the same!
Diagnosed with autism. Please excuse me if I miscommunicated anything.