Do all the “hidden” bones and skin slots affect overall performance?

EIvanov

I have a skeleton with multiple skins.
Skin 1 has one bone and one slot.
Skin 2 has 100 bones and 100 slots.
Similarly a bunch of bones and slots in skin 3, 4...100.
The skeleton is exported to unity, an object is created.
Skin 1 is active.

Do all bones and slots of all skins affect the overall performance when they are “hidden” and skin 1 is active?

Spinebot

When a skin is not active, the bones and constraints associated with that skin are inactive and do not affect performance. Only the bones and slots that are part of the active skin (in your case, Skin 1) will be computed and rendered. Therefore, having multiple skins with many bones and slots does not impact performance as long as they are not active. The inactive bones and slots do not require computations, so they do not contribute to the performance load.