There are a lot of interesting applications that doesn't require a "computational machine".. While the carbon atom example seems excessively specific, there are

There are a lot of interesting applications that doesn't require a "computational machine".. While the carbon atom example seems excessively specific, there are other setups like D-Waves quantum computer that works in a sort of in-between way, with programmable links between "atoms" so you can setup a custom Hamiltonian that should be minimized by the computer. That way you get sort of the best by both worlds, you get a (limited) programmability and you get easier observations than you would have access to just by for example designing a molecule encapsulating the problem you want to solve, as you would have to observe it "doing its stuff" somehow. Just because it can't crack crypto doesn't mean a large-scale version of a setup like this can't be valuable. The field of quantum chemistry needs to use huge supercomputer clusters to simulate stuff like this.