User search results from Graph API vs Directory

Hi,

I see that when I try to add a user to a site, Sharepoint gets results from the Graph API as well as from a Sharepoint API (/sites/DavidSite/_api/SP.UI.ApplicationPages.ClientPeoplePickerWebServiceInterface.ClientPeoplePickerSearchUser).

We're considering blocking access to the Graph API and would be interested to know what kind of user results are only available via the Graph API and not the above Sharepoint API.

Anyone have specific knowledge here?