I am not sure it is marketing
In itself the box doesn't help to sell the watch: for most people the box comes as a surprise. It is more so that it adds to the feeling during the selling/buying process. You don't buy just a watch, you buy a valuable timepiece, something luxurious, something important in your life. The box just shows that. I agree with Andrew, that walking down the street with that nice AD bag with that beautiful box in it, gives you an exciting feeling. And some anxiety too, so I almost immediately repack the whole thing in a huge bag, after which it looks like some luggage of a student coming home with his dirty laundry. I calm down in the hotel, where the ticking beauty is admired and inspected for the first time in any possible detail, The box too, and I don't hate it at all.
As written by me before, you only need excellent protection for the watch, and space for the watch and the paperwork. But it simply is not enough.
Kind regards,
Paul, wearing beautiful VC Portuguese (and I really don't even remember how the box looked like)