I just pushed commits for both the firmware and configuration GUI to add GiveBack support. GiveBack is a mechanism defined in the USB Power Delivery spec that allows the power supply to temporarily reduce power to one device in order to provide more to another. The implementation in the PD Buddy Sink works by removing power from the output when the power supply asks the Sink to reduce power.

"Why would I want my power supply to stop powering my device?" I hear you cry. GiveBack is largely intended for use in non-critical applications, such as battery charging. If a laptop is charging its battery from a USB PD powered hub while sharing power with an external hard drive, the hub power supply's limit could be approached during normal operation. If the hard drive needs to spin up, it will require more power than normal, which could overload the power supply. Making the laptop stop charging for a second while the hard drive spins up allows all devices involved to keep running without drawing too much power.

In short, if you're using a PD Buddy Sink to charge a battery, it would be polite to enable GiveBack to allow power supplies to manage their loads more effectively.