For those of you who don't know, it's the rate of compression of your music. The standard is 128kbps.

Most of my music on my <a href="http://www.geocities.com/dingojellybean2/playlist.html">playlist</a> are at 56kbps. Takes up 30-40% of the original space with little sound quality loss from 128kbps.

Since iTunes has a very enhanced media player(it primarily uses Quicktime Pro), the sound quality doesn't sound too noticable at 56kbps from 128kbps. So yeah.