OK, step back a bit. To use Spotify on Squeezebox players, then Squeezebox Server needs to be running on a laptop/PC/Mac/NAS on your home network.
The plugin-for Spotify needs to be downloaded and installed on whatever machine is running Squeezebox Server and yes, the stream will be the higher bit-rate used for Spotify Premium. None of this uses the Spotify client app you may already have on your laptop. (But, you could have installed Squeezebox Server on that laptop!).
Spotify on Sonos players is a different kettle of fish. The Sonos player(s) will login to the Spotify system directly.