If you're attending a regular-sized gym, you might be rolling daily with white through purple belts. You might notice how strength is less and less required as the skill gap increases. However, when skills match, strength matters yet again. This is why we have age sex and weight divisions. But why is it so?
Quite simply, I believe that with experience, one learns which fights are important to win, and which are distractions. For example, from the open guard, a novice won't blink an eye when someone controls both his pant legs, but will expend all his energy trying to bench press someone off of side control.
As my jiu-jitsu evolves, my fights become a lot more focused. With time, I have even learned a bit of anatomy. I know instinctively the parts of the body which are worth controlling, how much each joint is supposed to bend in a normal person, etc. I want to share this knowledge hoping it will help others. This is stuff I would have wanted to learn even before focusing on techniques. In other words, these are simply points of control which you either want to gain, or protect.
One of the most overlooked point of control are the armpits. Why is that control important? Because if you control the armpit, the person's elbow is not connected to his ribcage anymore. Fight to control it and suddenly the whole forearm becomes exposed for a nice kimura grip. Or use the underhook for your favorite pass and keeping the guy on his back.
Then, there's the elbow. The thing about the elbow is that it gives you leverage over the whole arm. Pull it through for chokes, or nullifying a side control escape, or arm barring. Another essential point of control.
If you're a guard player, you might also discover the importance of the knees. As long as you can use one knee to separate your hip from your partner's, you still have some mobility left for your guardwork. Don't let your knees get stapled to the mat, or even gripped, especially both at the same time.
I am sorry for the brevity, but keeping these things in mind has really made me more successful controlling stronger people, and if you know how to control these points, your jiu-jitsu will open up.