I don't know what would have happened if we just showed up when we were ready for dinner. It's one of the criticisms I have of the whole "freestyle" concept. If you knew in advance what time you wanted to eat each day, you may as well go for traditional seating. I have friends who sailed on NCL, and it was always jammed at the more popular dinner hours. They'd give you pagers so they could call you when a table was available. My friends tend to eat early, in the 5:30pm range, so they didn't have a problem. But for those who have late snacks or late arriving shore excursions, or for those who don't know how their day is going to unfold -- after all, they ARE on vacation! -- having to decide in the morning what time they want to eat dinner or risk a long wait at the door, it's not the most convenient thing.
The alternative of just going to the buffet restaurant when the mood strikes you to eat dinner is appealing to some.