It is important to clean your filters regularly so you do not have excess detritus building up in them. Detritus in your filter media, when it starts breaking down, becomes a nitrate factory which goes into your water column as the tank water is filtered through it. Nitrates and phosphates feed algae blooms. Just like vacuuming your gravel to remove excess detritus before it breaks down, cleaning the filters often will also keep the nitrates much lower. I guess if you do frequent PWC's, that would substitute for keeping the filters cleaner but if you cleaned your filters before they become completely clogged, it would make the water quality even better between PWC's. Further, the bacteria that is consuming and breaking down the detritus use up a lot of O2 and KH and put out a lot of CO2. The higher CO2 further feeds algae growth and lowers your pH. The loss of KH can cause your pH to crash putting your fish into pH shock.