Celebs on the grid.

What is the actual rational of teams/sponsors inviting so called celebs to and event as a guest and then allowing them to wander round the grid?
Indeed why do they get invited at all, do they in some way promote sponsor? If so then talking to the TV audience should be a must. Or are they there in some way to promote their career? If Alfa Romeo paid for Cara D something to be there, they did not get their money's worth as she seemed unwilling/unable to speak. ****ed, high or stupid?