It's actually a commonly held myth coming from a Revolutionary War era writing on military recommendations. The author thought it would wear the shoes better to switch back and forth as the soldiers marched, much like your tires today. However, it's a terrible idea and there's no evidence it was ever actually done. Straight last shoes (no right or left) were the standard for all shoes during that time, up until the industrial revolution made the shoemaking process so much cheaper in the mid-19th century. The use of right/left forms dates back much further, but it's easier when dealing with carved wooden heels to not need two different shapes, so straight last styles became a popular way to save money when heels were popularized during the 16th century. Straight last shoes form to the feet in just a couple of hours and it's just as uncomfortable after that to switch feet as our modern right/left shoes would be. Having studied numerous surviving shoes from this period, the wear patterns are usually distinct enough you can see the foot print on the sole.