This doesn’t mean that your AirPods will suddenly have Activation Lock, which is something that iPhones have. But rather, by linking it to your Apple ID, it will make it easier for users to locate their missing device, even if it is out of Bluetooth range and even if someone else might have found it and paired it with their iPhone.
According to the warning text discovered in the latest iOS 15 beta, “These AirPods are linked to your Apple ID. Removing them will allow another person to configure Find My Network. [ . . . ] Removing these AirPods will allow another person to configure Find My Network and it will no longer be linked to your Apple ID.”
This would also suggest that if you do want to sell off your AirPods, you will need to unpair them, or the person who buys it will have to unpair as well, otherwise it might potentially be used as a way to track people without them knowing. That being said, this feature is said to only be applicable for the AirPods Pro and AirPods Max, so those with regular AirPods will have to sit this one out.