The Customer tab allows you to add your customer details on the portal - a mini CRM if you will. When you add a Customer, their details like Company Name, ABN, Address, etc. will carry to the Services that you activate for them on the Atomic portal, which simplifies and possibly shorten the ordering process (as things like Address is pre-filled).
You can also add contact details and information should you have various contacts within the company. This is just a great way for you to maintain a list of all services that is associated to a particular customer.
For users that are using the Atomic platform as their outsourced billing platform will benefit greatly with this as invoices generated can now be even more seamless between the service you offer to your customer and invoicing them for those services.