Do non-rendered gameobjects use memory?

Do non-rendered gameobjects use memory? For example if I have enemies gameobjects w$$anonymous$$ch are not currently visible because player is far away from them, do they sleep? Or their components with Updates, FixedUpdates and all other stuff are running and use memory?

If theese gameobjects w$$anonymous$$ch are not visible on camera actually use much memory, then what is the best way to activate/deactivate them when seen/not seen?

thanks for answer in advance