There's also the cool factor.
"Celebrity is a tremendously powerful force," Clark said. "Everybody wants to say, 'Oh, I met George Clooney.' For the rest of your life, you get to tell a story that makes you look cool at cocktail parties."
But coolness aside, there's no question elite charity events do serious good. Elton John, for instance, has raised $125 million for his AIDS foundation through his various galas, including his famous Grammy and Oscar parties.
Alicia Keys has helped collect nearly $14 million for Keep A Child Alive, which provides AIDS treatment in India and Africa, with her annual gala. This year's Nov. 1 event will feature Keys and Beyoncé as performers and Oprah Winfrey and singer Angelique Kidjo as honorees. Tickets cost $5,000.
Most stars who participate in high-profile charity affairs are driven by a desire to give, but the ancillary benefits don't hurt either, says CharityWatch's Borochoff. "A lot of it does have to do with enlightened self-interest as well as the altruistic purpose."