I only trim pre-flowering for training/size management. After flipping to 12/12, I leave everything be… that said, I seem to be consistently having nitrogen deficiency around week 4-5 of 12/12, so some “natural” defoliation starts to occur around this time 
That said, my humidity in flower is generally quite low (< 40%), and I have lot of under-canopy air circulation… no pest or PM problems yet, fingers crossed.