What's the point of associating an Assist device w/ a specific voice assistant?

I have set up two different voice assistants:

  • The preferred one which uses Home Assistant Cloud and the default “okay nabu” wake word
  • Another one using a custom-trained wake word

I have two different Assist devices set up through ESPHome. One is linked to the preferred assistant, and the other to the custom-trained one.

My expectation was that each device would listen for and respond to their respective wake words, but in practice both devices will respond to both wake words.

So what’s the point of associating each device to a specific assistant?

Feels like I’m missing a key point or something, appreciate any insight!