Early in the Clone Wars, engineers at Rothana were busy building a new bipedal walker based on the successful (but expensive and thus rarely used) AT-XT walker. The earliest models were deployed late into the Clone Wars, but it was not until the formation of the Galactic Empire that AT-STs gained fame. Under the Empire, Balmorra became the center of AT-ST construction. Imperial commanders valued the walker's versatility: it excelled against infantry and lightly armored vehicles, and was also useful for protecting important units and patrolling hostile areas
While the AT-ST was designed to be effective on any terrain, its weakness against shifting terrain was exploited in the disastrous Battle of Endor. It was here that the native Ewoks found and exploited this as well as several other key flaws in the AT-ST, leading to most of the walkers on the planet being destroyed. After this battle, AT-STs were forbidden from being deployed on extensively forested worlds or worlds with natives that were armed with primitive weaponry. The Imperial Remnant would continue to use the walkers, though not as extensively.
The AT-ST is one of several light vehicles in the game. Imperial Remnant light vehicles are primarily devoted to anti-infantry duties, and the AT-ST is no exception. The 2 blaster cannons rip through infantry, and being a walker the AT-ST can also crush infantry. The AT-ST is also heavily armored, able to withstand heavy firepower for a short period of time. In addition, the AT-ST is the only unit in the game to have the Barrage ability. When active, the walker stands in place and unleashes a nearly continuous line of fire. This greatly increases its damage output and can even be used against heavy vehicles.
There is some disagreement as to whether the AT-ST or the AT-PT is the better unit. The strengths of the AT-ST are the extra armor and ability to Barrage Area. These abilities combined allows it to take on much larger targets than conventional anti-infantry units. It is also slightly cheaper than the AT-PT, though the cost difference is hardly noticeable. However, it sometimes has trouble maneuvering into position to fire. Use the AT-ST if you are a player who wants a heavy infantry destroyer that can tackle much tougher opponents, but will require some micro to bring out its full effectiveness.