One more point for consideration.
As @Steelers36 so accurately described above, an FCD (Future Cruise Deposit, not to be confused with a Future Cruise Credit - altogether different beasts) is used to make a DEPOSIT on a cruise you are booking.
When you use an FCD that you have previously purchased and have in your FCD “bank” as a deposit, you are making a deposit in the amount of exactly $100. Stay with me here….
It’s not unusual when booking a cruise to find a deposit requirement of $800 or more. Without an FCD, you will pay whatever the listed deposit amount is to secure that cruise. But if you have an FCD to use, your deposit amounts is $100 no matter what the listed deposit amount is on the payment page.
All this plus it’s easy to get a $100 OBC when you use an FCD.
By definition - free money