It's the law, here in Swizzerland you have to stop at stop signs, normally they just stand where you can't foresight if someone is coming or not, thats why you have to stop. Also, people are idiots and some just pull out if they can't foresight what's coming, so it might be a little safer that way.
Here, if someone is already in the intersection he has the right of way and if it's a normal 4 way with Stop signs or no signs on all ends its right before left.