The use case for this is primarily when you initialize the contract and need to send out the first sales invoice. Navigate to the the Recurring Billing contract view page.
Click the "Create Billing" button
This will advance the "Next Billing Date" based on the frequency chosen.
Also, the "Last Billing Date" will be updated with the value that was in the "Next Billing Date" field prior to clicking the "Create Billing" button. This provides an audit trail of when the contract was last billed and when it is supposed to be billed next.