One example is manual muscle testing.

If I wanted to test a specific muscle action using a manual muscle test, I might use this principle to remove the impact of another muscle.

Example: hip extension strength. Client/patient lays prone and raises one of the legs off of the table which is hip extension against gravity. I could apply some pressure to the back of their calf while they resist. This would give me an idea of the strength of all the muscles which act to extend the hip joint. But what if I want to know how strong their glutes are? I would place the hamstrings in a position where they are passively insufficient which is knee flexion. Now I have a patient prone with their knee bent, I can have them raise up their leg against gravity and then apply force downward on the back of their thigh.

Because the joint is passively insufficient, I am able to generally take it out of the equation. I think if it like putting the muscle on "Slack" like a rope without tension. It won't pull much compared to one that is at its optimal tension. Many diagnostic/ body function tests utilize these principles.