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.
Not often enough and yes. And then error 9 after the heater shorts out when the top up salt warning stops working :/ Fortunately the pump with integrated heater strip is relatively easy to replace.
I hated those heaters. The most common failure point. Made a lot of money selling them, though :D
And replacing the pump/heater assembly on a Bosch/Siemens is harder than on Indesit/Beko/Whirlpool. Have to fiddle with a screwdriver and a flashlight from the side.
On that note, the drainage needs cleaning often (or the sensor whines about it), and I liked the water flow sensor (which they use instead of a pressure switch) on Bosch/Siemens.
I've only had to do it once (3yr old machine), maybe every 2 years or so? Never seen error 24; I can just tell by ear when it's slowing because our air-gap seems to amplify the sound of draining water.
