Right, they serve no purpose except on that rare occasion when they prevent your rear derailleur from catastrophically going into your spokes because it somehow got slightly bent and you didn't know it. Sort of like an air bag on a car--they hardly ever get used.
Not trying to sound high and mighty--l've taken the disks off all of my bikes, too. But I sometimes wonder of that was such a good idea. I guess this is one of those times.