Just curious. How did the Muslim tactics differ in this regard from the tactics used by the Romans, Byzantines and Persians? By anybody else at the time?
Ancient and medieval warfare were not for the squeamish.
The difference was in how the conquered peoples could join up and become full partners regardless of race, ethnicity, location etc. This made a compelling case to flip sides, especially for the wealthy and powerful. They could retain their wealth and position, even get a promotion as a reward for turning traitor early as an example. Just say the shahada, take a Muslim name, and welcome aboard the team. Like the mafia but easier to join. This was very different from the Roman citizen model. Need I go on, really? Is this all new to you? Seriously? Are you just teasing me? Really?