You mean the filter at the bottom? Ideally you want to do it every time. Bosch/Siemens have an interesting way of measuring the amount of water: Other manufact

You mean the filter at the bottom? Ideally you want to do it every time. Bosch/Siemens have an interesting way of measuring the amount of water: Other manufacturers (and older BSH appliances) use a simple pressure switch. Bosch went all German engineering with a fully electronic system. The intake has a propeller with magnetized blades and a reed switch that counts the rotations, so it knows exactly how much water goes in, which is pretty damn cool. The turbidity sensor in the drain plays a vital role in this - it assures the mainboard that the dishwasher is, in fact, empty. Otherwise it would overfill. And because of that, BSH dishwashers are very trigger happy with the drain errors. They could also be caused by pieces of food/glass in the drain pump, btw. Surprisingly, this over-engineered solution is more reliable on a dishwasher because a traditional pressure switch gets clogged more often and is harder to fix.