With one email address, we cannot login to multiple organizations of Service Desk Plus Cloud.
With one email address, who has already joined to another organization cannot to join our organization. We cannot do what we can do in the other cloud service such as "Salesforce".
We use it in communities to build an ecosystem with several companies. With each own one email address, we want to make "ServiceDeskPlus Cloud" available in various domains, regardless of the service usage in each company.