Yes, this is absolutely necessary in order to achieve proper functioning.
If a motion detector is installed on each floor of a staircase and you want to ensure that the light in the entire staircase is only switched off when the last motion detector no longer detects any movement, then each one must be registered with each one. It is not sufficient if 1 is registered with 2 and 2 with 3, but 1 must also be registered with 3.
In combined operation, must each motion detector be registered with each?
