There are elite gymnasts who do not use grips, so one could say you never NEED them. That said, as a bars coach, I usually recommend grips when a gymnast is training Level 5, has a decent kip without grips (i.e. understands how to shift her wrists over the bar), and is starting to swing on the high bar. With smaller or younger gymnasts, I don't always recommend grips, as they may not have a good enough grip on the bar or may find grips cumbersome. Also, some Level 5s have tiny hands and skinny fingers can't fit conventional grips. With older and heavier gymnasts, I sometimes let Level 4s wear them, especially if they are prone to rips and are uptraining tap swings or other swinging skills. Ultimately, it's usually up to the coach.