I use it sometimes for callbacks that take similar but not exactly the same arguments, f.e. containers for pointers that can have an optional "release" function

I use it sometimes for callbacks that take similar but not exactly the same arguments, f.e. containers for pointers that can have an optional "release" function pointer that is called to release all pointers in the container and can be assigned to "free" for raw data, or object specific destructors like "free_bitmap" or "free_sound" or even "free_container" (so having a container with other containers inside that may have their own "release" functions).