Reloading has been around basically since the beginning of the country. Back then men would pour black powder, stuff wadding, and pour shot down the barrel of their musket. They were not often hungry . This is proof that reloading is effective, no matter how rudimentary.
When self-contained shotshells became available, handloading did not stop. In the east store-bought ammo was readily available but in the west this was not the case. Early hunters and shooters in the west, because of the lack of readily available store-bought ammo, by necessity, were reloaders
Despite this, shotshell reloading did not really come into its own until the 1950s. At that time the design of shotshell reloading tools reached a point where the process became a fairly easy thing to do.
The new self-contained tool designs eliminated the need for multiple and often crude devices that the reloaders were used to.
There are several million reloaders today; of which a small percentage is metallic presses fitted with adapters to accept shotshell dies. These are generally used to produce small amounts of hunting loads. A larger percent are single stage that can produce enough ammo for a limited amount of shotgun sports and hunting, and save some money to boot. Serious shooters, that shoot a lot of shotgun sports, are apt o use a progressive reloader as they can produce several hundred rounds an hour, and in the process save some serious jack!
Regardless, all shotshell reloaders share some common interest, besides saving money. The most important is probably assembly of safe ammo that does what it is suppose to do.
Sometimes reloaders ignore the assumed goal of safe and sane reloading often due to ignorance. The reloader who wants to reload safe, high performance ammo can learn by reading and following the directions and recipes of reputable reloading manuals.
It is my opinion that a shotshell reloading manual is far more detailed than one combined with metallic data. The main topic is metallic data with limited shotshell data thrown in.