Well, the way I understand it is this.
...mind you I'm just a novice....
Panning a sound places that sound in a particular space within the soundstage (i.e. stereo spectrum)
If you try and put the guitar and vocals(which are usually center in most modern recordings) in the same spot, things will tend to sound cluttered and "smaller" since both of these things also will be sharing much of the same frequency spectrum.
Putting the guitar to one side or the other will lessen clutter but tend to skew the balance of the recording.
So splitting the guitar to the left AND right leaves room in the middle for other things , like vocals(conventional focal point) and/or bass ( conventionally anchored in the center, but in a different frequency range from the vocals)
However, duplicating a track and panning left and right can actually thin the sound a little but will usually sound pretty much exactly the same as mono center, IF both tracks are exactly the same.
BUT, if you EQ each a little differently, or put just a smidge of delay on one, than you can cook up a fat and tasty Big sound and still leave room for other things in the middle of the soundstage.
(like a solo or something)
Of course you could just record two tracks seperately, and a lot of good players will, but if you're like me then you will rarely get every note timed correct and flams can be distracting.
So bouncing the track, or even better, double tracking the take can ensure you that the playing on both tracks is locked dead-on.
This is really good if you have some good interplay going on between the guitar and bass, for axample, and then in the conext of the overall mix you want a broader sound for the guitar.
If you are four track recording this will force you to compromise some of these options.
Remember though, you dont neccessarily have to center everything. Look at Van Halen one.
-mike
