The 3dsmax UI only allows you to set material effects ID up to 16 channels. The VRayMtl allows you to go beyond this using the effects ID override but other types of materials don't have any UI to adjust this. This tool using a backdoor into 3dsmax to set the effects ID beyond the 16 limit imposed by the UI.
This means you can create masks for every material in your scene. Using this tool you can either assign effects IDs by hand or just press to automatically create them and their mask render elements.