My guess is it's just there to make it clear that they didn't forget the signal, just aren't using it.
Pros and cons. What if you have multiple such signals? High risk of accidentally connecting them together.
I'd recommend leaving unused outputs unconnected as long as the tool allows it.
On the other hand, NEVER leave unused inputs unconnected, even if (as is the case more times that I would like) the tool does does allow it and does what you would like it to do in response -- the real world isn't nearly so forgiving.