Baffles break up the flow allowing for micro bubbles to dissipate before reaching the pump. Also, they prevent things from getting into your pump, like chaeto and micro bubbles.
I also use some of my baffle for filtering and I place sheets of filter media there to catch small debris. I only have to change it when it is dirty and since I have a pre filter, that is only like every few months.
Baffles also separate the compartments in the sump like if you have shrimp or crabs living in your fuge, it'll prevent them from being were they aren't supposed to be. The snails won't stay though... lol I have to move mine around.