I defoliate periodically in veg, whenever I think a leaf is in the way., but I do heavy LST training too.
I have had great responses from my plants to defoliation - check out Karen and especially Nesia for good examples in my diaries.
Do not defoliate "just because" that is pointless. Instead only try to defoliate where there is a good reason to do so.
Defoliation strategy and techniques have been proven to increase yields and alter timings, the more you read, research, and practice, the more you will come to value this highly useful horticultural practice.