Often thralls are used for decoration only. If we were able to switch between active and passive thralls, we could use them as decoration and at the same time reduce server load. A passive thrall could have its normal inventory, but would not interact with enemies. It just stays at its given place, performs its default animation. If in need the player could reactivate it and use it as normal thrall, as long as his total number of active thralls is below a certain limit.