How billing account administrator role different from the billing account user and why?
Let’s say your organization is set up where you want the primary developers to be able create new projects and enable APIs to use as resources in those projects. However, you don’t want them to be able to create new billing accounts or change how the billing accounts are being paid for.
In this scenario, you would give your primary developers the role of Billing Account User (roles/billing.user) and Project Creator (roles/project.creator) so that they could assign a specific project to an available billing account – which would allow them to use APIs that require billing to be enabled. The Billing Account Administrator (roles/billing.admin) chooses how a billing account is paid and configures billing exports; they can also link/unlink projects from the billing account – but they can’t view the content in a project without further permissions.
Hope this helps!