Disney doesn't lose out, but other people trying to make reservations would, if people were to do this all the time.
I'm not talking about this particular person holding two for what seems to be a reasonable reason on only one night.
I tried to get into Chef Mickey's, CRT and 1900 Park Fare and couldn't at 2 months before our trip. I know they book early and I don't mind if all those people who booked before me, actually do plan to eat there, but it would be frustrating to know we missed out because somebody double booked a bunch of reservations on purpose and then cancelled last minute the one they decided they didn't feel like using.