When triggering a switch or light, some products expect a parameter to be passed defining pre-set options… For example, Pool Lights have a pre-set of colors to choose from and the API for Aqualink doesnt support RGB but instead expects a color choice number… so when switching on the light the user needs to pick a color from a list of 12 colors… Names like Emerald Green, Disco, USA… etc… In the light component there would be a definition of supported color schemes which are presented in the HA UI as a input select… similar to the Effect List feature of lights.
There is similar functionality with the Input Select component (https://www.home-assistant.io/components/input_select/) but that cant be included in a Light components interface or pre-canned in a platform specific component.