I believe you need variety to gain both strength and size, but also to keep your sanity.
If you always do 5-8 reps or whatever, you'll lose your mind after a while (in my opinion) as well as if you always do few reps like 1-3, where your risk of injury increases or if you do 10-20 where your risk of boredom increases exponentially, etc.
My personal opinion is that you should progress in a linear pattern where you go from 10 reps to 2 reps then test, or do something like staying in a certain rep range say 5 reps but increasing the weight or lowering the rest times until you have to reset.
Something I have noticed for me is that if I go from lots of reps to few reps and vice versa, so I would be going from a high volume like 3x 8 to a low volume like 3x 1 and vice versa alternating every few months, I seem to keep making progress.
It has been said you need high reps to make muscles bigger and give you room to grow, but you need low reps to fill out those muscles with denser muscle mass to get stronger. Do only one or the other, and you may get size or strength, but not both.
I believe that was the joke JD was making about sarcoplasmic and myofibular hypertrophy that might have flown right by.