If you've heard athletes talk about "muscle insertion points", this is where and why they matter.

To get a little mathy, the formula governing how much effort is required to move a resisting force around a third-class lever is:

Effort = Resistance * (Distance to Resistance / Distance to Effort)

where distances are calculated from the fulcrum.

In this formula, "distance to effort" is in the denominator. What this means is that to move the same amount of resistance, at the same distance, we require half as much effort if we double the distance between the fulcrum and the load.

In our joints, that "Distance to Effort" is the distance between the joint and the insertion point of the muscle - that is, the point at which the muscle attaches to the bone across the joint. So for a bicep curl, in theory, if your bicep were to attach further from the elbow joint, you would need less contractile effort from the muscle to lift the same weight than if it were attached closer to the joint.

I don't know if the variability between athletes is great enough to be practically meaningful, and I don't see insertion points brought up as much as they used to be, but conceptually they're significant.

(Source: https://www.engineeringtoolbox.com/levers-d_1304.html )
(And for reference: https://www.healthline.com/human-body-maps/biceps-brachii)