Im up to help! :3
@InstallGentoo: It occurred to me that the band that plays at the CFM concerts is a good example of this. The roles that each instrument plays will vary between songs, but the band instruments are composed of:On a similar note, some people break their instruments/song components into different categories, like bass, leads (often higher-pitched than bass), drums, chords, etc. Having an instrument or two that covers each area is seen, in this theory, as a good starting point for building a song.