Accounts should be created by domain owners to group domains that share the same administrative boundary. For example, if your company has 10 domains, they can all be in one account. If you are a developer with multiple customers, each customer should set up their own account and add their domains, and then grant you access to their account.
An issue you will encounter is that is it impossible to grant Dashboard access to a subset of domains within an account, it is all or nothing. You can grant more granular access where it is via the API.
After setting up my account and the first domain I’m then able to add extra domains to my account and select which plan ( Pro/Business/Enterprise ) each domain is to be on.