If you are selling a site or domain in the marketplace that is not currently being used for anything (I assume mostly domains, since why would you take down your site?), you can do a wildcard CNAME for it to park.digitalpoint.com if you want. If that is done, anytime someone typing in your domain (maybe to check on domains they might want to buy), they will be automatically redirected to your sale/auction page for the domain. Nothing too exciting, but I'm sure some will find it useful when they have long-term auctions/sales looking for a buyer.
No, it's not for domain verification... Otherwise anyone could verify other people's domains since there isn't anything unique about it.