According to Google, “Today, we’re making it easier for people to connect Fast Pair compatible accessories to devices associated with the same Google Account. Fast Pair will connect accessories to a user’s current and future Android phones (6.0+), and we’re adding support for Chromebooks in 2019.”
Basically the idea is that if you were to buy a new device like get a new phone or tablet, you will be able to pair existing devices like headphones and speakers easier, as long as those devices share the same Google account. In a way we guess this is like how your devices remember your “profiles” so that you won’t need to set everything up again when you get a new phone.
As Google notes, this will require Android 6.0 or later, which safe to say is the majority of Android devices, so you shouldn’t be left out of this feature unless for whatever reason you’re still using a very old Android handset.