You save everything. You keep the buds to smoke (you will want to do some research on how to trim bud and cure it). The rest of the leaves and stems you can use to make keif, hash, wax, oil, etc.
You can but the leaves do not have as many Trichomes on them. The Trichomes are the glands that contain the THC. It is MUCH better to stick to smoking the bud which is high in Trichomes. You have to smoke a lot of leaves to get the same effect. It is much better to just make keif out of them. It is easy to do and you will have some nice stuff to sprinkle on your bowl.
AND, you can compost the remains! Seriously, search for dry ice hash. So easy to do. Why waste the Trichomes?
I was reading about making a tincture on another thread. I love rum. A high proof one with the extra trim let it sit in the freezer shake it up and filter it so its drinkable. Sounds great and its better than wasting it.