I've seen pictures of people doing that, though it's definitely not a necessity, as they would have come with a stock cooler from the factory. As for benefits, I'd say the best you'd see is a slight increase in stability, though 'see' is relative, as you won't notice it...
i.e.-if you have some sinks laying around, go ahead and slap 'em on, it doesn't hurt, but is it worth the $9-$20 for new sinks...probably not.