If you're not sweating, you're probably "cheating" by not fully immersing in the asana!
I think that depends. HOW you work is as important as how much you work. Beginners generally have not learned to surrender and thus add unnecessary effort to their practice. As your practice matures, the capacity to surrender (among others) can increase, reducing the tendency to strain. Learning to release the outer body more and work more internally is part of this process. Keep in mind that we tend to reinforce our existing tendencies. People who always tend to over-do will tend to approach their yoga the same way. Utlimately, every pose, as Mr. Iyengar says, can be restorative. Look at the general direction of your practice. Are you developing a greater sense of ease? Are you finding more of what the Iyengars call "repose in the pose"?