Its not about how much it can hold. When you add baffles, you create sub sections.
If for whatever reason you tank stopped draining to the sump from the overflow. With no baffle's the return pump would pump ALL of the water up to the tank, which more than likely would result in a flood.
When you have baffles, because its compartmentalized, it will only pump a small amount of water back to the tank, which would probably not flood your house.