Subway...

... are very, very strange. At least the one closest to where I work is.

Now I am by no means a marketing expert, but the little I have gleaned, is that the main purposes of promotions / special offers are as follows :
1/ To get people to come into your shop.
2/ To get people already in your shop to spend more money than they would have otherwise.
3/ To get people to come back to your shop, and spend more money at some future time.

There may possibly be other more secret reasons that I am not aware of, but these I think are the main ones. Now, given these assumptions, and also given the following :
1/ This Subway store is quite out of the way, so no passing trade would see any promotional posters etc in the windows.
2/ There WERE no promotional posters in the windows.
3/ Subway sandwiches cost between £3 and £6 depending on the size and what you have on them

Could somebody now please tell me the logic behind the following offer, as it's been confusing me since lunchtime:
"Buy a large drink for £1.20 and get your sandwich free".

Now as I've already stated, this offer was not publicised, and therefore no-one would know about it until they were actually in the shop. So the sum total achieved by this? My conclusion was that I went into the shop to buy a sandwich, got it cheaper than I was already planning on paying, and got a free drink...

I'm really not at all sure what Subway get out of this deal...