"Well, there are physiological benefits, obviously: You use your lungs in a way that you probably don't for the rest of your day, breathing deeply and openly. And there are psychological benefits, too: Singing aloud leaves you with a sense of levity and contentedness."From NPR's "This I Believe".
I agree; singing and harmonizing with a bunch of friends is fun. But remember, if you pick songs like "Love hurts", which appears on Eno's list, only one of the two can survive: the song or the friendship :)