I find when I practice off mats my right shoulder starts to hurt midway thru hitting buckets, and then to (somewhat subconsciously) ease the pain, I develope an ouside/in swing plane, end up undercutting the ball, and developing slice swing tendencies that carry over to the course. If all the area courses are on mats (because of growing/maintenance issues on the grass portions), then I generally prefer to play super twilight and kinda practice on the course.