Can I use WHMCS without connecting to the reseller server?

My Web Design & Hosting business has grown to the stage that I need to make invoicing more automatic.
Payment has been bank transfer and the occasional cheque.
Now with WHMCS I've reached the Paypal level of payment (to be setup).
When I take on a new client they register and accept my TOS without buying a product.
I then generate an invoice.
I charge yearly for hosting and there are 3 design payments - 50% at the start, 25% after 1 calendar month, 25% the next calendar month.
Domain registration is handled outside WHMCS at the moment.

My question is -
At this stage do I need to set up the server connections?

I resell on 2 non-connected CPanel/WHM servers.
What are the advantages of connecting WHMCS to the servers?
From what I have read WHMCS will handle terminating accounts etc does it do anything else at the server?

I'd appreciate comments to help expand my knowledge of this side of the business, and help me properly use WHMCS

thanks

Rob