Walls that can drain and dry last a lot longer than walls that stay wet. An air gap (a rainscreen) between the siding and sheathing lets both dry independently.
There are many ways to create a rainscreen gap between the back of the siding and the drainage plane of the wall (WRB, exterior insulation, surface of ZIP sheathing); here are at least a few options—on paper and in the real world, as well as some background rainscreen information.
