I wore a Donjoy brace for the first 3 years after my 1999 meniscus operation. Then I lost about 20 lbs and started doing leg exercises, presses, etc. at the gym. When the bigger leg muscles do heavier exercises the muscles hypertrophy. Exercise magazines and books say that the support structures, secondary muscles, ligaments, tendons, etc., also all build up. From my experience it felt and looked as if everything built up, same with arms. These support structures tend to make the joint tighter so that it probably moves in a more controlled way, less lateral wobble, etc. I also stopped using the brace at that time although I probably could have done so earlier.
For effects other than on the main muscle exercised, see second paragraph, -
With arthritis I am not sure that heavier leg exercises don't do harm. ? With acutely injured joints I have read that isometric exercises are sometimes used to maintain muscle while healing.
A Dr's advice and perhaps a prescription for some physical therapy for safe exercises would be best.