Ok, first off, out of all of our trips to WDW, I have only double booked ADR's for one of those trips. It was in December of 2008 and you have no idea how much stuff that I was juggling in attempting to create a workable itinerary for us being that my MIL was going to be touring the parks with us. She has a host of health issues, dietary issues, and more. It was done because at the time, Disney had not released the CP packages yet and I needed to make sure that we had a plan in place based on who the CP narrator was going to be on whatever day it was that we were going to be at Epcot. They kept swapping out the dates of who was announcing on what day and the package details took forever to work out. So, my MIL had ADR's under her room reservation for one plan and I had ADR's for our room reservation for the other plan. Technically, we did not double book in the eyes of Disney because these ADR's were booked under two separate reservations and under two separate names. It involved about 3 days worth of our 10 day trip. Once the CP packages came out, we made our decision on which day was the right day for us to do CP, booked the package that we wanted, and then cancelled all of the other ADR's that would not be used. This was done ASAP, so that many other people had the benefit of grabbing up those spots for themselves.
Yes, this was self serving. I wanted to make the last trip that my partner and her mother would share at Disney special. The trip had it's good moments and it's not so good moments, but I know that I did my best to make it work. I will not ever feel bad for doing what I did because in the end the effort was made to make two other people that I care about happy.
I do not double book ADR's for our trips together. There is no need. I have the super planner gene and can plan out a WDW vacation in a matter of hours right down to which ride at what time and pretty much when the bathroom breaks will fall. I don't condone double booking ADR's as a rule. I do see how certain circumstances can make it seem more necessary as an exception, rather than the rule of how people plan. Some situations just don't fall under the regular way that things work and not everyone knows enough about how things flow to plan appropriately 180 days in advance.