The B1s were perhaps the most numerous (and expendable) soldiers in galactic history and, unlike most organic soldiers, they were capable of operating in hostile environments such as underwater or in space. They were designed, for the most part, to defeat their enemies through numbers, not through their ability to think (they were very vulnerable to tricks) and use combat skills (unlike clone troopers).
The B1 battle droid was frequently used as a Trade Federation soldier. As a result, the B1s were present in almost every battle that involved the Trade Federation.
The first battles involving the droids required a central computer for the droids to think, but this was mostly removed after the Battle of Naboo after an attack destroyed the mainframe stationed there, resulting in the deactivation of all the droids of the planet.