I think it depends on the level of the player and how confident they are in their mechanics. If you're working on your stroke and it hasn't yet become a habit, then it would not be a good idea to not think about it in competition. Your unconscious mind is liable to cause you to revert back to your old stroke. I've seen it happen over and over again with students who revert back to their old strokes without even realizing it and then wonder what happened.
I would consider myself an A- player (high runs are 6 racks in 9-ball and 91 in straights), and one of the biggest problems I have in competition is a tendency to overthink ball speed as opposed to letting it happen. Conversely, when I just visualize the shot and trust my arm I get there much more often. Your thoughts ? What's the best direction I can go to improve on this?