A public school official once told me that their school system owned 50 Ipads which were stored in a closet, unopened for over a year with no plan of use. This struck me to the core, and I often think about it whenever I lead an educational activity that has a near-zero cost. Now I won't claim that working with cardboard covers the same content as a tablet based curriculum might, but I'd be happy to share other near-zero cost ideas that would.
I know this isn't the most rigorous educational exercise, but I have no problem defending the claim that the children learned new and important ideas during these programs. First, for almost all the students at every age, it was abundantly clear that this was the first time an adult had ever trusted them with a knife. It was also clear that the teachers present still did not trust them with a knife. After letting hundreds of students cut cardboard with knives, one cut their finger and needed a band-aid. Everyone should learn from this, but I have a feeling the lesson will stick with the kids more than it does the adults. Second, building three dimensional objects from two dimensional materials is a process required by nearly every act of construction, and getting to know this idea by working with cardboard is an excellent way to prepare to do the same with your material of choice. New knowledge is built on prior knowledge, so if you want to build a shoe rack, your experience of building a cardboard boat will help.