The Delta E Rewards certificate for r/t coach discount excludes fares booked in L or U, valid for 6 months from issue date, 48 states only, 14 days advance purchase, Saturday night stay required, 30 day maximum, non-tranferable, not combinable with other certificates, awards,vouchers and promotions including upgrades and has blackout dates.
Sure doesn't look like a great value with all those restrictions.