Sure, I don't see any reason why a person building their own house shouldn't be able to, say, run a garden hose from the gas meter, across the lawn, under their slab, then up the wall to their furnace if they want to.
Or why bother with PEX and those complicated fittings for your water, why not just run garden hose in your walls and attic for your water?...Some people would if they could.