Why have teeth in baffles of sump?

[Chappy]

I'm making my own sump for a 180 and am wondering why have teeth routed in the baffles? I noticed in the bubble traps there are no teeth, but the refugium does have teeth. Is it to keep snails or macro from getting into the return?

 

[Lincutis]

exactly. It does put the water level below the top of the overflow to discourage creatures from taking a ride.