Doubling a track does not mean taking one signal (i.e. one mic) and recording it simultaneously on two tracks. You could pan both dead center or hard right and left and they would sound identical. If you record the same thing (e.g. a rhythem guitar) twice, one on each track, and then pan them left/right, its the small differences between each track that tells your ears there's one guitar way on the left and another on the right, giving you a huge soundstage, even though they are playing the "same" thing. Or you can take one source, record it direct to one channel, and send a delayed signal (say 20-40ms) to the other, and then the delay will still create the illusion of difference which widens the soundstage.