At certain times, Much like missions, You may unlock special 'Side Scenarios', where any number of things could happen. There's really no way to tell what will trigger it until it happens, but If it does, it can often be quite helpful...
The types of Special Scenarios are here:
Let's Split up Scooby Gang! - When in a group of NPCs, if your character suggests a split up, then you temporary gain control of one or more of the NPCs your character was with to find more items or goals.