Delta has a unique gift-giving scheme when you achieve your elite Medallion statuses, dubbed Choice Benefits.
When SkyMiles members first achieve Platinum status, they are allowed to choose a gift from a list of choices, including upgrade certificates, and more.
Achieving Diamond status yields 2 gifts, and the gift options differ between the statuses too.
For example, for Platinum, the upgrade certificate gift includes 4 regional flight upgrades, while for Diamond it is 4 global or 8 regional flight upgrades. You get an extra gift just for being Diamond as well.
One gift exclusive to Diamond status is upgrading an individual Delta Sky Club Membership to an executive membership.