Key distinctions made above:

Solo riding, brake use depends on level of nuance the rider brings to the road. Highly experienced riders will use brakes whenever and however useful, usually without much thought and never a problem. A less nuanced rider may use brakes at lower speeds and less lean angle and still have trouble. Usually low-side washouts, but I've seen a couple of folks stiffen up and high side things. Nasty.

In a group, predictability requires that individuals not do something different from the group. In general, this is why I don't do club rides. The corners are especially weird, with many different lines and braking patterns. Have to give everyone lots of room.

Certainly braking in a turn when someone is following may seem rude to the following rider.