On any Delta flight that runs out of OH space (even if the bag fits) you can check your bag at the gate for free and pick it up at the carousel. Sometimes they ask for volunteers before boarding. We don't usually call this gate checking a bag (see below).

On the smallest of aircraft, where the bags don't fit, you can "gate check" the bag and pick it up at the arrival gate (not carousel).

Neither has a charge. With the early boarding you get with your card you will not likely be forced to check the bag to your destination.

The gate checked bags are pink tagged and remain airside (through security). The checked bags go off to the other world with the normal white sticker tag. Get what you need out of the bag (keys) if this happens, JIC.