When I am practicing (home), I shoot rather fast--excepting for a few shots that need real mental energy. I miss shots that would have easily gone in. Here, if I screwed up, I reset the table and shoot it again several times to reinforce the proper execution of that particular shot. I take a mental note to slow down when playing for keeps.
When I play for keeps (league) I slow down, consider the options, plan the shot, chalk the tip, then get down and execute. This brings my play up to where my game is most of the time (more so in the early games of a match than later games for some <as yet undetermined> reason.)
When I play for fun (at the bar), I shoot somewhere between fast and slow. It really doesn't mater if I win or loose, its just for fun. Last weekend I lost once in 4 hours.
ETA: I'm 58.8 yo.