Like most when playing alone or just for practice, I leave flagstick in.
Playing for score I would want to be sure that the flagstick was centered, which means you need to inspect the hole or have some else. I have seen where the flagstick was leaning either because it was replaced incorrectly or something causes it to lean. So it would seem to be a bit careless to just go to the ball and put without first checking.
I have 2 round in for the year and anything outside of 4 feet I have left flagstick except sharp side hill breakers. When practice putting short putts I always remove the flagstick. Can't explain why but leaving it in affects my accuracy (probably due to head case).