Using release instead of focus is somewhat of a gamble. There is a good chance you will get some out of focus images. I can live with that.
For me it started as a necessity because my daughter's indoor karate tests had so little light and contrast that I was missing shots waiting for the focus to lock. Since I knew that most photos would be taken at a similar distance I changed the setting to release instead. The trade off was missing some shots as being out of focus, but at least the shutter was firing. If you have enough DOF, you can miss focus by a bit and still be okay.
Outdoors I've found focusing to be fast enough in most all situations that I rarely miss shots from lack of focus (unless I lose track of the subject). I also shoot in bursts of 3 to 5 frames at a time. So even if the first shot is not in good focus, the later shots in the burst usually are in focus.
If you can track your subject well using AF-On, and keep your subject in focus, it should not matter if you have a1 set to focus. Nor will it matter if a1 is set to release.
My theory is that if I am shooting action photos (sports, wildlife, etc.) I want the shutter to fire when I press the button, period. If I have time to ensure focus is locked, that's fine. I will wait and be patient in taking shots. But if not, any shot is better than no shot. I'd rather have a chance at getting "the" action shot rather than missing it altogether if the focus isn't dialed in to the camera's liking.