A filter does cut down on the plenum and ducting getting real dirty.. Mesh Filters used to work great but they were done away with by the NFPA... The regular baffle filters work good , but we are talking about cooking 10 to 15 hours or more a day for between 90 to 180 days.. Man thats alot of grease.. I think it would be a good idea for someone to come up with a better filter system, although it would cut down on the vent hood cleaning frequency which would be bad for the hood cleaning business...