By adding a voice file that can understand a specific schema, developers enable their favorite assistant to control virtually all similar things that are translated to that schema.
The alpha version provides a few samples voice files for Cortana to control lights, window shades and thermostats. We would love to see the community add more voice files for Cortana for different categories of things, as well as for other assistants such as Alexa etc.
Voice files could also be added to understand multiple schemas, thus enabling assistants to control all similar things that are translated to each schema.