It is NOT obligatory and some would say you should never defoliate (I'm not one of them!).. You want to do defoliation for a reason... to get more light to lower bud sites or to improve the air movement through your grow... if your grow is really dense, defoliation will help avoid bud rot. If you choose to do it, do it slowly - i..e., a little bit at a time because you don't want to overly stress your plant. I've had some that are really sensitive and others that didn't care if I took 90% of the leaves off in one day! You will need to do a little, wait a day to see your plant's reaction and make the call as to whether you need to do more and whether she tolerates it well....
Good luck!