Processing the Full 3D takes an extremely high amount of RAM to do so. At best, it is four times as much memory as the the normal, 2.5D processing.
We are upping it slowly because this high memory requirement significantly affects our job scheduling and prioritization.
We still are not totally sure that we are going to keep the feature because people have been unhappy with the results mostly due to improper data collection for it. Nadir images will not do a good job. It works well if it you do it right, but until we make an app to fly properly, people will keep messing it up...