This is required for 3-way or 4-way switching.
If I make all my remote control relays “Form C”,
also called SPDT, or “Single Pole, Double Throw”,
always identified by 3 connections,
(N/O, Normally Open), (N/C Normally Closed) and (C Commutor)
this allows “normal” switch operation in the event of a total “home automation” failure. The 3-way switches will just operate as normal switches.
A good electrician always makes sure that all 3 or 4-way switches on a lighting circuit are in the relaxed position (down) when the light circuit is off. 3-way and 4-way switches have no “On” or “Off” markings.