It's to draw contrast to "design systems" like Gridfinity, which is based on boxes that are multiples of 42mm on each side.
There are tradeoffs between the two approaches, with no real "right" answer. Gridfinity trades some flexibility for compatibility, the 42mm squares mean you can move the gridfinity boxes on a base without reprinting anything. This gives you much more flexibility, but if you want to change the size of one part you'll have to reprint a bunch of things.
There are tradeoffs between the two approaches, with no real "right" answer. Gridfinity trades some flexibility for compatibility, the 42mm squares mean you can move the gridfinity boxes on a base without reprinting anything. This gives you much more flexibility, but if you want to change the size of one part you'll have to reprint a bunch of things.