well dont take my word as the golden word but IMHO I take the entire leaf minus maybe a half inch away from plat stem. I have not run into any problems as of yet and this is prob the 4th grow that I have been doing this. I really should have started snipping sooner than I did on this grow but when the body says no sometimes you really have to listen. I read somewhere that a grower was doing the trimming right through veg and into flower as to keep stress down since it would be spread out over the entire grow but I try not to interupt veg to much. By trimming I can honestly say that the yeild seems higher, the entire plant finishes at the same time instead of top then bottom a week later and at harvest time most of the leaves are gone already so it is a matter of seperate buds and throw in spin-pro then done.