Duration of notes
Very often a guitar piece has a melody line, bass line and some accompaniment, for example the famous Romance Anonyme.
It might be sensible to have at least three layers: voices or channels in this case. We'll explain why. See the example here below. Click on the image for a better view.
To accomplish a high level of reality you should be aware of the proper duration of your notes. Generally it doesn't make sense to insert a Pedal Down controller (CC64), simply because a guitar doesn't have any pedal. The effect wil be very artificial, if not just awful. So in many circumstances you'll have to adapt durations in an intelligent way (manually).
This could result in more "layers" : staves or voices when you use notation software, because all information in one stave or voice is just not clear while working on your project. The triplet notes in the accompaniment have a duration of a quarter note actually, so this part should have two voices or layers itself. So we have here one stave for the melody, one for the accompaniment and one for the bass notes in this example. It could have been done with only two staves, but then you will need two voices in your notation software.