Since moving to NorCal, I have never seen anyone practice on the approach doing things to work on a specific part of their game. I see many practice sessions like league bowling - scoring.
When I do practice I sometimes get +/- comments, I get looked at in whatever way, and/or people are interested in what I am doing. And, I always go alone if I am going to work on a specific part of my game. ALL the guys I practice with are interested in scoring, so I follow. Also, I think it's a $$$ issue too???
Anyway, my last sesssion was for spares. So I played low (score) ball and 1/ games - (try) hit 10 pin only, then spare the rest with strike ball. Other days, I'm standing near the foul line doing whatever I had planned that day to work on release, swing, balance, etc....
In Washington where I've bowled leagues several years ago, I'd see towels on the approach or past the foul line. I see guys/gals bowling without the ball, or even better, NO PINS. Thumb white tape down the lane, or a quarter taped on the 10th board 38' away. But I never seen these types of practice sessions in my current area unless that person is working with a coach.
What I find that's funny is when bowlers complain they practice a lot but never improved like they had hoped.....