Well balls, literally. Had a random bagseed at home so thought why not clone it and put them out to replace the slug killed plants... yeah except its male so now i got 10 male clones vegging, woohoo.
It's a balance between the new trichomes coming into maturity and old ones starting to degarde, there is no right answer as personal preference makes such a difference.
With sativa dom strains you can expect it to stretch a lot while flowering, if your grow room is 2meters then you should flower at 0.66m or below. You can LST and FIM to bring those branches down. The idea is you create a bush with multiple main colas all at the same height, this increases yeild...
Trimming is best when done gradually, take a few leaves every few days to reduce shock to the plant. Start with the leaves at the bottom that get least light.