I don't know if you'd call it an aiming system as such. I use mostly ghost ball and back of ball aiming, but I have noticed certain regularities in how the shots react from various angles with different speeds etc. So I do have a systematic way of compensating for that, involving precise aimpoints inside and outside the pocket. These are not random compensations but carefully calculated from trial and error, knowledge of throw etc. I use these when I'm coming onto the table cold etc, then the instinct takes over once I'm a couple of shots in. There are a handful of shots on the table where I feel I get some benefit from aiming with a commercial type system, and on those I will sometimes use them.
I have used aiming systems in the past and can use them if I feel like it, but I think they get in the way of playing the game for the most part. They may have their uses for shots that can deceive you, and for the inexperienced player, but once you start running the balls, I think it's rare for people who actually play well, to be mechanically applying an aiming system.