Your filter should be inspected at every oil change interval. In “normal” driving conditions, change every 20,000 km. Unless “severe” conditions such dusty roads, then change at 10,000 km
The cabin air filter can be compared to your home’s furnace filter as it acts in the same manner, trapping dust, pollen, pollutants, etc. Over time, these filters become contaminated and blocked, thereby preventing clean air to enter your car’s interior for you and your passengers to breath.