Would point out that on a recent cruise on the Edge, there were a couple of nights when the 4 MDRs had separate lines for those with reservations and those without. This was the first time I had seen this on an E-class ship. Once seated, one could see many empty seats in the restaurant(s), so it would seem the issue was one of staff capacity, not seating capacity. Long waits (45 min +) to be seated for dinner on Celebrity are rare but do happen from time to time (maybe 5 or 6 times over 11 cruises for me) with all or almost all of those being on "evening chic" nights.