If you squat 30 rep's without any weight making sure that you move smoothly and without pause, maintaining constant tension on the muclses being worked...which is a lot, then it's actually quite difficult and extremely uncomfortable and painful...
You're pretty good if you can do three sets of thirty.
It does the body good to do this often.
But I now really believe that you'd benefit from training correctly, that's if you intend to be doing this for a long long time.