Why does disabling an object eliminate its transform performance cost?

Questions & Answers
1

I have a parent object with a child object that has several hundred box colliders attached (why I have to do it this way is a long and frustrating story). When I move the object, my game naturally falls to about 2 FPS. When I disable the child object, the object moves as if nothing were ever attached to it. When I stop moving it and reactivate the child object, all have the colliders have followed along.

Why is updating the transforms of disabled objects so cheap performance-wise?

2

When you move an object Unity has to calculate positions of each and every child each frame you change the position of parent object. When object is disabled Unity doesn’t give a damn about those calculations and only moves enabled objects. When you enable your children, Unity calculates the position change only once and moves the children directly to that position

Edit: Note that it’s massively simplified, but that’s the general idea