What is the point of having more than one Mii?
When you add other Miis to your account, they will occasionally show up in background places while you are playing Miitomo.
So far, I have noticed that they can appear:
- At the register when checking out from purchases
- In the 'loading' screen before the game is booted up
- In Miitomo Drop as Miis that you can drop to try and get special items
- As additional characters in MiiFotos
Other than that, you cannot interact with them in any significant way.