It can be used to start a large and varied conversation, although has been known to be a conversation on it's own:
Person 1: "Yes!"
Person 2: "Yes."
*end of conversation*
"Yes" is very handy to use if you don't have time to talk to someone, for example if you are in a hurry to get somewhere but pass an old friend along the way. By exchanging "yes's" in a couple of seconds it is as effective as stopping for a cup to coffee and a chat about good times.
A word of warning, if you use "yes" as a greeting outside of Derry, you will generally be given funny looks...
2) An expletive shouted out during an orgasm.
3) A British progressive rock (or art rock) group known for their hits "Roundabout" and "Owner of a Lonely Heart".
4) A brand of laundry detergent in the US.
2) YES! YES! YES!
3) Let's listen to Yes.
4) I need to wash clothese, where's the Yes?
Around the South Side,
So cold that we cried
Were we ever colder on that day!
A million miles away
It seemed from all of eternity!