Said behavior causes a lot of framerate lag when a lot of entities exist in the world. Whether or not the player can see them.

Disabling said behavior with a mod did not change how anything looked.

Testing might require an override of the entity collision code to disable it on client side to see effects on fps.
With it being limited to server only 4k mobs (non-visible) can run 60fps.
With vanilla behavior framerate tanks even when the mobs aren't visible.
The same calculations are effectively done twice.