Like all filters, they need regular maintenance.
Mine gets the filter floss changed every month or so, the sponges squeezed out in siphoned tank water and the like.
And some of it is part of bio-filtration, the bacteria colonize the filter media so rinsing it with the sink can sometimes cause spikes in your ammonia/etc as the bacteria recolonize.'
I've learnt the hard way that if your HOB doesn't get cleaned enough, it can plug up and overflow enough to pre-soak your basement carpets for washing lol.