You should Opt-in if you want to maintain peace of mind when purchasing necessities (prescriptions, gas, etc.) or when you have an unexpected expense (need your car towed, go to the emergency room, A/C needs repair, etc.) and there are not sufficient funds in your account at the time the transaction is being authorized.*
The Courtesy Pay program could save you from an awkward situation when paying for services already provided (restaurant, hair salon, etc.). If you choose to Opt-out, these transactions will be declined when funds are not available.
*This free program is discretionary and opting-in does not guarantee transactions will be approved if funds are not available. The full amount of the overdraft balance plus related fees will be due immediately, but in no event more than 20 days after the date of the occurrence.