jkwilson has the answer. The whole reason for the pole barn design is; cheap and long-enough-lived. This style survived because for the price, you get the strength and utility needed during your tenure as a... farm, shop, whatever. The treated posts will last in ground (and our ground is...
RossABQ has an unbeatable argument but, if you want the max insulation and are saving 2/3 then doubling the thickness is still a 1/3 savings and more "comfort". The truss co. can add an extra board to the bottom cord or if stick-building the same for the ceiling/floor joists. There are some...