This feature is designed for a multi-site setup. You can auto-redirect the user to a specific Identity Provider (IdP) for SSO based on the domain name of the site from which SSO is initiated.
For example, if you have a multisite setup with 2 sites. One site is for teachers and another is for students with users stored on two different IdPs, then this feature will automatically redirect them to their respective IdP based on the site from which they initiate SSO.
Steps to configure this feature:
Navigate to the Signin tab of the module.
Check the option - Site Domain Based SSO (For multisite setup only).