The basic idea is that cadence is a result of the important factors of power, torque, and the rotational inertia (I am not a physicist, that may not be the exact proper term).
People often say low cadence is bad for your knees, but it's really that high pedal force (torque) without building up the supporting/stabilizing muscles, ligaments, tendons, etc. is the problem.
A low cadence, by itself, is not necessarily a bad thing. If I am just cruising at a nice easy conversational pace, for example, I will be riding at a low power and low cadence. If I am riding tempo, I will be riding at a higher cadence and moderate power. And if I am riding hard, I will be riding a high cadence and high power. In those situations, my pedal force will all be fairly similar.
But do you know where you want to be for each situation? Isn't watching your cadence for any situation a way to verify that you are where you want to be? If your power tap died on a ride, would you be able to be about where you wanted based on using a known cadence for that situation? I get it's an end result. But when, in general, most people end up in the same range in a given situation, doesn't an end result basically equal a desired result?