Cups dont have to be changed. The contents can be. SO in my case i stuck bags of rock rubble in mine, and i can throw a bag of carbon or chemipure in there if needed, or even polifill after a waterchange to catch any large particles. I got sick and tired of changing socks on my old tank every 2 days. The biggest thing with this tank, was i wanted to employ the less maintenence, more enjoyment approach. I sized my ATO tank well, and went this way, so i can not tinker with it constantly, and actually enjoy it.what is the advantage of filter cups over socks?