The website implies this is if you elect for an ecredit instead of a refund if there’s a schedule change or significant delay or cancellation.

The website says ecredits are still good for 1 year if you voluntarily cancel:
If you voluntarily cancel your flight (without a significant travel disruption caused by Delta, as outlined above), your eCredit will be valid for 1 year from the original ticket date, minus any applicable cancellation fees.
https://www.delta.com/us/en/booking-...t-cards#expire