For me, I have a total of 99 dragons in my hibernation cave, so I can only fit one more, and I can't afford to have it at its maximum as I need that one space when I have to move a dragon for breeding. So, when I get an egg I already have I can't place it anywhere. Not in a habitat or in the hibernation cave. Therefore I have one of two options, sell it for quick $ or display it on a pedestal. Once the egg is on the pedestal, I can't hatch it, but at anytime I can cash it in for $. I've decided to display eggs simply because I think they are cool. It adds character.
You're on my friends list, so I'm sure you've swung by and done a sweep of my party hats. It's a personal thing, and it's all about how you like to decorate your islands.