Effective Jun 1 of last year, the deposit requirement for suites through the Future Cruises Department is the same as booking online. In most cases 10% deposit is required. So the only benefit for booking onboard is the extra OBC.
If you purchase a Book Later option for $100 pp and then use it later for a suite, you have to pay the difference for the higher suite deposit so that loophole is gone.
For more information: link