The official benefit is status guest + one other in the same room.
I’ve never had anyone travelling with me denied free breakfast though (never been anywhere in the US).
I pretty regularly do me + another guest in a different room, never been a problem.
A few times I’ve done me + someone not staying at the hotel (e.g. breakfast meeting)
The most I’ve ever done is me, wife, two kids (across two room) + two colleagues (across two more rooms).