DEMCI filters are so fine that I can actually see dust collect on them in as little as 48hrs. A visible circle, the size of the fan (or in my case, 3 140mm circles on a 3x140mm magnetic filter). All it takes to clean them is to literally just wipe your hand across them, it just rolls off easily. My house is clean, though sometimes a little untidy. Its amazing how much dust is in the air in even the cleanest environments. Hepa filters are completely unnecessary, but basic fine mesh filters are a must if you don't want to do the whole air compressor/brush declogging process every year. A clean computer, particularly clean fans and fan cooled heat sinks, runs a lot cooler. It astonishes me how some old machines I've fixed up for customers have even still been running, with dust turning heatsinks into solid blocks of dust and detritus.