Originally Posted by cordelli

My thought - Garlic bread is often offered to mask the fact that the rest of the food is pretty bland and boring. By filling you up and overwhelming your senses with the butter and garlic, you don't notice the rest of the meal isn't up to it.

It's pretty much an invention of the Italian American restaurant, outside the tourist areas you probably won't find it that often in Italy (though you probably won't find that much pasta either)