Thanks for posting! The "No Rebellions" setting means that your units and cities will not rebel during the game. The rebels who start the game in play represent enemies within your own house, minor houses, and others who will oppose your rise to power. They are not impacted by that setting.

Activating "No Rebellions" gives you greater freedom in handling your economy, converting people to your religious sect, raising taxes, and skimming the tithe.

Let me know if that answers your question