Did you know that a pole has twice the bending strength of a dimensioned piece of wood the same size?
Shipbuilders used poles as masts for sailing ships. They removed very little wood other than bark to maintain mask bending strength.
As a tree grows, it prestresses its fibers. Wood on the outside of a tree trunk can achieve 2000 psi of tension. The inner wood is actually in compression. The outer tension of the exterior wood is what allows a tree to bend substantially before it actually goes into compression.
A post, used in modern post frame construction, acts in the same fashion when embedded in the ground. Forces of nature are transmitted into the ground enabling a very strong structure compared to other forms of construction.
Smaller structures use 4x6 posts, 6x6 is the most commonly used post in many areas, 8x8 are used in the pacific northwest and Florida. Laminated posts are manufactured units that are surfaced on all four sides, so straighter than a sawn post and resists twisting better. These units are stronger than a sawn post dimensionally too.
So, now we know why pole barns using post frame construction are so strong compared to traditional platform framing.
Modern concrete structures use this same technique to strengthen them against breaking under tension.