The two-by-fours at your local home center are not 2 inches thick or 4 inches wide...not anymore at least. They spent several weeks at that size though. The sawmill cut them to that size to stack and kiln dry, and then when removed from the kiln they are then milled straight and square. Used to be they would sell the rough stock to carpenters who would do the milling themselves, but then they figured out that the railroads were charging them a fortune to ship a lot of wood that was going to be ground to sawdust anyway, so they started milling the boards before shipment. Same amount of construction lumber arrives at the construction site and it took less fuel for the locomotive to deliver it.