Plants can not "direct" energy, all energy is used equally wherever there is growth occurring.
All of the plants energy is made in/by the leaves.
so.........
Maximum amount of healthy green leaves = maximum energy production = maximum growth.
or.........
less leaves = less energy being made = less growth.
If you want maximum yield, leave as many leaves as possible.
Potency is dependant on genetics, but the healthier your plant, the better it is able to express its genetics.
Forget trimming and concentrate on keeping your plants as happy and healthy as possible and they will do the rest.
Besides, if your plant would not need those leaves, it would not grow them in the first place!
Stick with 18/6 too, this is optimum for cannabis.
Hope this helps, Organoman.