Together, these rules constrain the space of possible solutions, preventing errant matches and zeroing in on the correct ones.
I think it's interesting that our brains rely on certain assumptions about how the world works to make sense of what we're seeing. These rules seem pretty effective most of the time, but I imagine they could also lead us to misinterpret things that don't follow the patterns we're used to. This could help explain why visual illusions happen, since our brains might be applying the same rules that normally help us perceive the world accurately, just in situations where those rules don't quite work.