The speaker signal comes in on the input terminals, goes through one relay and comes out on one set of the output terminals. The other set of output terminals have their own relay paralleled to the input terminals.
The only other connections internally is the 150 ohm 5 watt resistors feeding the headphone jack.
It is a convenience for those folks with two sets of speakers and only one output terminal set on their receiver.
No additional protection advantage, or anything else, is conferred.
Gettin a bit antsy there Bob? According to tracking at 10 am it arrived in Phoenix.