What's the difference between scheduled revenue and unscheduled revenue?

Revenue is scheduled when Receivables creates, for a transaction line, the revenue distribution records for all accounting periods as specified by the revenue scheduling rule assigned to each line.

Scheduled revenue doesn't mean that the revenue amounts are already earned. It means only that Receivables has created the distribution records for these amounts.

Unscheduled revenue is deferred to an unearned revenue account. Revenue remains unscheduled either until you manually schedule the revenue or an event triggers the automatic recognition of previously deferred revenue, for example, the customer makes a payment.