Torque2 and jb5000 are my answers too.
I will add that the beacon for us has to be on even for just towing.
If the grnd crew know the aircraft is almost ready, normally when last pax door is closed, they will connect to the headset waiting for crew call.
Any lengthy delay then crew also use the beacon to attract attention of the grnd crew to contact the cockpit and give pre pushback clearance.
All the checklists I have seen include 'beacon on' as SOP.
I await all the comments and differences with other companies as there are many I am sure.
TW