I designed this box as a container for corrugations (one of the pictures shows such use, for Monument Valley Corrugation). Some corrugations are springy and will unfold if not forced into shape by a box or a frame.
The problem with many designs, such as Plain Box, is that the thickness of the walls uses up space inside the box. This makes external dimensions easily controllable, but inner dimensions not so. Such boxes make nice lower parts of two-piece boxes since it is easy to match them to the lids’ sizes, but they make bad containers whose internal dimensions need to precisely match some predetermined size.
With Predictable Box, it is the other way around: internal dimensions come out predictable at the cost of external dimensions, which is a desired property when folding a box supposed to contain a corrugation.