Play Store like Galaxy Store uses two keys/certificates.
Author Key tells the store who developed the app and how to contact them.
Distributor Key tells your device it is OK to install your app on that device.
For WFS these keys are kept in an encrypted file and you put the path to it. It should be in your users folder. It can be the same folder you use for GWS or one specific for WFS or a simple username/keystore folder.
Android developer are often teams building multiple versions having an key alias for each developer or project is useful.
As far as I can tell you can use the same distributor Key and Key Alias for several devices but each device would be a unique key. The Author key remains the same for all devices.
Hope that helps,
Ron