I've tried AF lock on occasion but this to me would seem a bit cumbersome because you are constantly keeping track of when the camera focuses and when you want to keep that focus (or not) by either releasing or holding down the AF button. Why not just use AF-C if you are concerned about the subject moving? The camera will still lock on focus and keep it there even the subject doesn not move.
Using AF-C together with AF-On is a very useful technique. AF-C is great for keeping subjects in focus even if they move, but in certain instances, where you want to place the subject outside of any selectable focus points, or when you have very little time to switch the AF points, the use of AF-On together with AF-C can be very useful. So pretty much this method will still give you the ability to focus and recompose and still have AF-C handy when you need it.
The only issue is to get used to working this way, that the shutter release and the focus acquisition is de-coupled.
BTW, this is used a lot by many wedding photographers, especially those who shoot with primes and ambient light. I use it from time to time in my work too.
