One thing I can tell you: everyone who has them IS wearing them in the wrong place in softball!
How should they be worn?
They are supposed to be worn on the bottom two straps of the knee guards so that you don't put stress on the knee joint. The closer they are to the knee, the more they will work as a fulcrum and pull the knee apart.
If they're sitting on them in one of their receiving stances, then they're relying on them. They're probably good for younger kids, and newer catchers who are developing. But (my opinion mind you) they should be doing strengthening exercises, which would eliminate the need for them.