Breath Awareness Meditation

I have noticed that many meditations start with breath awareness, I wonder if the purpose of that is to get us in touch with the autonomous system in order to realize that there is no effort in breathing? Concerning the process of go into the gap, could it be explained as get in touch with the autonomous system. From what I know about this system it makes sense to me that, no effort (we do not have to concentrate to do it), no attachment (as we are not expecting to breath) is required.