If you use the Sonos App to play music on your speaker, it will use the music account service installed in that App. If there is more than one account from the same service, it users whichever one you last selected as default. 

In the above case, you will find that you can leave the house with your mobile device and the music will continue to play as the online streaming service communicates directly with the chosen Sonos speaker(s).

There are however other ways to play audio to Sonos products from a mobile device using the ‘Airplay’ protocol for example and a music streaming App on the mobile (such as Apple Music, Spotify or Deezer etc.) In that instance, the online streaming service goes via the mobile device to the speaker and so in that case the music service account on the mobile is used, rather than the ones in the Sonos App. If you walk out the house with the mobile the music will stop playing just as soon as the device leaves the WiFi network and the audio buffers drain on the Sonos speaker(s).

Thanks @Ken_Griffiths 

So even if I use my own Soptify account standalone or via the Sonos app, when I go out the house (walking the dog) and open Spotify on my mobile to use with my headphone, the One speaker in the house will be effected by my choices (Both myself and the One in the house will play the same music I choice or will stop if I stop the music)? I assume it’s because both are using my Spotify account?

I use Android so no Airplay, but my family use Airplay and can take over the One when I leave.

I will run some experiments as it is a bit confusing.

Cheers

Mike

In your case Mike it appears you are using Spotify ‘Connect’ which uses the Sonos API to play to your speakers when the device/App is authorised on your local network . 

I don’t use that type of connection very much, but apparently you can leave/walk away from that local network with an open ‘Connect’ session left intact and start playback on your home speaker when outside the home, until you, or someone on the local network with their controller App, ends the Spotify ‘Connect’ session. 

Playing something to a speaker from the Sonos App for example will terminate any previous Spotify ‘Connect’ session on the chosen speaker, or you can switch playback in the Spotify App back to your mobile device.