Is some light defoliation required or should I let them live freely?

Hi. So day 21 of flower usually is a cut off zone, if you are before it, its perfect time ! But think twice, are your plants healthy, maybe couple leaves off and tucking , plus small clearing of bottom would serve you better ? If you still positive, that too many buds don't get light or you expect high humidity levels later in flower - do it ! There is plenty articles how , when and what. You can check my 8 sisters diary , week 3 and 6 of flower. Do it before watering, always leave fully formed set of leaves, take off all matured lower. Good luck !