Syncing two entities state, so that they always work together. Without the need of creating a automation to do the syncing. One example is a binary_sensor that i use to turn a light on and off. I had to create an automation to achieve this. Where i could simple sync up the light state with the state of the binary_sensor.
Maybe this is what you’re looking for?
It can be used as a wrapper around the binary sensor, so your light and binary sensor will have the same state.
Why would you need to have a second entity having the exact same state than another at any given time?
I probably don’t understand what you’re trying to achieve, so you might need to clarify your example, which doesn’t examplify the why or what.