I share the concern of most people here...
I have some friends that head to WDW about every other year for about 2 weeks at a shot. They actually make ADR's for lunch in every park, every day and also ADR's for dinner in every park, every day. Then, once they get down there, they just go to whatever park they feel like on any particular day and they have reservations for lunch and dinner.
This means that for a 10 day trip, they will actually use 10 lunch reservations and 10 dinner reservations. However, that also means they will no-show for 30 lunch reservations and 30 dinner reservations!
That drives me crazy and I keep trying to get them to change that behavior, but they are just stuck in that mindset.
At least I can make the choice to never travel there with them!