Four instruments, not four tracks.
If it were four tracks, I'd often be limited to one guitar, and sometimes go way over four tracks with one guitar if I'm layering MIDIguitar softsynths in stereo. ? Some things like drum programming and softsynths often take up three tracks by themselves, but only produce one instrument. Hell, I'll often have each drum on a different MIDI source track and rack up a dozen of those.
A single instrument "comped" out of multiple takes still counts as one. As long as you don't have layered guitar sounds from different takes, calling it one. If it's two guitars layered (even in unison), it's still two guitars and counts as two.
BTW: I've been thinking about raising the limit from four to six. How would everyone else feel about that?
I feel a bit guilty about it because maybe if I were a better player then I wouldn't need to break the thing up into so many pieces.
When it comes to recording, it's an acceptable way of writing music and improving your recordings. The important thing IMO, is being able to perform your part live. Comping an instrument is fine as long as you learn to play the comped part (I often end up with comped solos that I have to learn to play after I've recorded them (and it makes me a better player).
Even with layering, it's used as a sonic "texture" thing (think Jimmy page - the master of the art), and the basic part can be played live, without losing much (the texture would get lost live anyway).
