Food: Margarine

I've been wondering lately why we put butter or margarine on our sandwiches. (Although I'm told by some Americans that it's less common over here.) Is the spread an adhesive, to hold the contents to the bread? Is it a lubricant, to help the sandwich on its way down your gullet? Is it just for the taste?

Here's an American cookbook from 1837 with directions for making a Ham Sandwich (including buttered bread!). (More sandwich recipes from old cookbooks.)

This Yahoo forum discussion points to sandwich-buttering being a non-American or older person thing.

Visit the website of the British Sandwich Association (British Sandwich Week starts May 14th).

Wikipedia has a good article on margarine - apparently Big Butter conspired against margarine by promoting bans on adding colouring agents to artificial spreads. (A ban is still in effect in Quebec.)