A mix, by definition, is more than one track. In other words, you mix the guitar track with the bass track and the drum track and the vocal track. For anything other than very simple recordings (for example, a live vocal/guitar) I record everything in mono, then create stereo when I mix it down. For example, the vocal typically goes to the center, rhythm guitar to one side, lead guitar to the other (subject always to change). There's no reason to record a track that will end up in a larger mix to be recorded in stereo. Not only do you waste hard drive space, but the mix gets muddy pretty quickly. It's not about what one part sounds like, but how it fits into the mix.