The best use case for leveraging the existing SAML integration to connect Salesforce with other internal systems is to make Apex SOAP outbound integrations to external web servicesmore secure. SAML can be used to authenticate the Salesforce org as the service provider and obtain a session ID from the external system as the identity provider. This session ID can then be used to make SOAP calls to the external web service without exposing any credentials in the Apex code. Option A is not correct because formula fields with HYPERLINK() do not support SAML authentication. Option C is not correct because Apex REST outbound integrations require OAuth or basic authentication, not SAML. Option D is not correct because API inbound integrations from an external Java client require OAuth or basic authentication, not SAML. References:

Named Credentials as Callout Endpoints

SAML SSO with Salesforce as the Service Provider