I maybe should add that on long tours (multi week or multi month) I have always managed to have a flexible end date. This helps avoid the need to have a rigid schedule and avoid needing to schedule days. Getting air travel up front by riding toward home may help if you live near one end of your tour.
In general if the purpose of a zero day is recovery, I find that a litlle mileage is better than none to accomplish that. I generally ride every day at home these days so it is even more natural to do the same on tour than it was back in the days when I couldn't ride every day at home, but I always tried to do that on tour.
Planning days off to do interesting or fun stuff is another matter. I probably should do more of that. I can't say I regret spending days sitting in camp or worse yet a motel room.