Sorry... I didn't mean to be so cryptic. By mechanical filtration, I mean anything that removes particulate matter from the water column and traps it in some disposable or (preferably) rinseable/cleanable medium. With messy fish (like cichlids), a lot of mechanical filtration allows you to capture and export fish poop, uneaten food, other organic stuff BEFORE it is attacked and broken down by bacteria. This can greatly improve water quailty by keeping nitrates and other compounds at lower levels, meaning you'll be changing less water.
I suppose some might say I go overboard, but I don't believe you can overfilter a tank, esp. a cichlid tank. You have to be careful you don't go overboard and create too much current, but the more mechanical filtration you have, the cleaner your water and the healthier your fish -- provided you change/clean the filter media.
Does that make more sense?
Jim