Joining VCSA to AD vs add as Identity Source

Hi,

In VCSA I can add an Active Directory Identity Source which would allow me to set permissions to specific Active Directory Users to the vSphere environment.

Therefore what are the reasons why one would join the VCSA to the Active Directory Domain? And what about the hosts managed by the VCSA?

Undoubtedly, this would bring in disadvantages...such as what happens if Active Directory is down, will everything fallback to local authentication?

Thanks