Most plants lie in a group that are harvested differently to other plants. Is it like tea, where different leaves provide different grades, or do flowers and leaves and stalks get separated? Presumably the more woody parts will go to hemp-like products (clothing, paper, beer, whatever!). The industry around that exists already but will presumably be developed ahead of other countries if demand makes for a lot of 'waste'.
Presumably, modern farmer techniques like indoor vertical farming might produce better yields.
The valuable part is the flower. Plants need to be carefully groomed (preferably in a closed environment) to sex them immediately and kill any males, to prevent seeding. (Seeds are a sign of poor quality control.)
Stems, leaves, and trim are probably just composted, although I suppose leaves might be processed to extract oils.
I recently visited Colorado on vacation, and got to visit a few legal dispensaries with my pothead companions (I'm not, but they are). It was a remarkable experience. Everything is totally focused on quality, and product differentiation for the marijuana itself was all about the best possible product with particular desirable characteristics. With few exceptions, price was a flat rate of $220/oz across the state. So maximizing yield is not nearly as important as maximizing quality. This is a connoisseur market. There was also a strong market for edible products (cookies, candies), oils, and other extracts.
It's also mostly an indoor crop. When I was in Oak Creek, a tiny town in the mountains, my host pointed out four different "grow room" buildings, basically urban farming operations.
It was interesting to talk about it with my host's fiance, a retired cop from Detroit (who is a part-time local cop there now). He thinks it's great, and marijuana laws in most states are just wasteful and stupid.
Presumably, modern farmer techniques like indoor vertical farming might produce better yields.