Security defaults make it easy to protect your organization with the following preconfigured security settings:
Requiring all users to register for Azure AD Multi-Factor Authentication.
Requiring administrators to do multi-factor authentication.
Blocking legacy authentication protocols.
Requiring users to do multi-factor authentication when necessary.
Protecting privileged activities like access to the Azure portal.
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/fundamentals/concept-fundamentals-security-defaults