Hmmmm, I'm going to go out on a limb a little bit here and disagree about roving being the best practice.
I think the better form of practice is shooting a 3-D course at unknown distances. I realize the unknown distance part is significant portion of the "roving" aspect, however when I hear of guys going "roving" through the woods (and I used to do it quite a bit), it was typically picking out small targets, often with a unique feature that draws your concentration. "Let's shoot that red leaf over there. Let's see who's closest to the black spot on that stump. Let's see who can hit that little clump of grass accross the gully." Aim small, hit small comes to mind. Yet when that deer walks in front of you, it doesn't have that little aiming spot to concentrate on. When you walk through a 3-D course at unknown distances, you have to work on both distance estimation and concetrating on picking a spot on a large target that may not have any unique "aiming" points; just like the real thing.
Anyway, I think that roving is very good practice. I'm just saying I don't feel it's the "best" for the above reason.