Travel agents probably know about this already, but Royal Caribbean is making some changes to it's onboard booking programs, effective March 15.
Previously, if you made an 'open booking' by buying a future cruise certificate while you were on a cruise, for a $100 deposit you got an unassigned booking number with OBC that varied based on cruise length, but offered $100 for a 7 night cruise. The new program drops that down to $25 for 7 nights. If you book a specific 7 night cruise then you still get the $100 OBC, however if you later change that specific booking to another ship or itinerary Royal Caribbean 'reserves the right' to adjust the OBC to the levels offered for an 'open booking', meaning if you decide to change your booking to a different week but on the same ship and itinerary, suddenly your OBC will drop from $100 to $25.
Cruises booked while aboard will offer different amounts of OBC that are based on cabin category. Book a Grand Suite for a 7 night cruise and get $200 OBC. A balcony cabin is $100. Oceanview is $50 and an inside cabin is $25. Again, this is for a specific cruise and not just an open booking for some future cruise yet to be decided.
Bottom line is that is seems the "Next Cruise" open booking certificates are not going to be as worthwhile as they used to be. The new OBC levels start at $25 for 5-7 day cruises and top out at $100 for cruises of 15+ days. So, either book a specific cruise and stick with that booking, or I suggest just forgetting the whole thing and not bother with booking while on a cruise any more. The benefits are definitely being diminished.