Just by Nature of how I hunt I'm not always in position to have a good rest. I like to lean off of a tree, but not always an option. So I practice off hand, resting on my knee, laying prone, sitting. ANyway I might have to shoot while in the field. I shoot of a good rest and bags to get sighted in and when trying to shoot for groups, but in actual practice I'm using hunting positions.
In the field, the shot could come at any time, so I try to be ready.
-Jake