When I train kids who wear them, I do not make them take them off. Mainly because I think a good intending parent spent money for the betterment of their kid. BUT, I always tell them that they have limited value, and if they choose to use, keep them low. Sometimes, you will see catchers that wear them higher than the bottom strap, which actually does harm! The White Sox catcher, Tyler Flowers, actually does this and I want to scream to kids, "do not watch".
Old catchers with old knees find some relief using Knee savers...but that's about it.