We've seen FD take it's toll on ADR availability and quality of service because it seems to strain the system. Everyone is trying to get their money's worth, so they book a lot more TS/ADRs. Even some (but not all) of the restaurants that you could normally walk up to will be booked ahead of time. And there can be a lot slower lines for QS and snacks and people ask for all their options at each stop. In the past, we've been there as FD starts or ends and you can definitely see a change (we used to try and avoid FD time periods as a result, but it keeps growing to cover more of the year). But it';s been a couple of years for us, and FD room availability is less and less (spread out over a wider time period) as the crowds have shifted, and most of the earlier effects (more tables crammed in TS restaurants; more limited menus) are now permanent regardless of time of year.
If anything, the servers are generally more relaxed and happy when they find out they don't have to explain the
DDP to you or answer a lot of questions, some of us here have noticed that OOP service is often be cheerier and/or better than for the DDP customer at the next table.