If enabled, then aircraft on the ground will not be shown on TCAS and will not be forwarded as multiplayer aircraft to 3rd party plugins. Both (TCAS and multiplayer) happens via the same technical mechanism, so it can't be separated. Use this option if you want a more realistic TCAS behaviour (as in reality a/c on the ground do not typically appear on TCAS) at the price of not seeing ground a/c in 3rd party plugins.