Business Unit Allocation when using SAML

I have want to enable SAML on my IriusRisk instance, do I now need to manage allocation of BU's through our SAML configuration? 

No, there are two ways to manage BU allocation, the feature of assigning BU's via SAML attributes is completely optional. You can still manage your business units natively if you wish to do so when enabling SAML within IriusRisk