Essentially, in a mature biofilter, only the surface area on the outside of the media is really usable in most circumstances, unless the media has some way to stay clean, flush mulm and flush old inefficient layers of biofilm.
Bioballs, will very rarely clog, but only has aerobic biofilms colonizing its surface area as it has no internal pore structure to utilize for de-nitrification.
Sintered glass medias will not appear to clog (apart from visible mulm deposits) but as biofilms build up, the internal pore structure not only gets blocked, but as internal flow is reduced, any bacteria that may be residing in the internal structure of the media cannot get oxygen or water flow to bring the waste to it that it is designed to digest.
Marine pure also, like bioballs, very rarely clogs, because the holes in the pore structure are much larger (visible to the naked eye) the water can freely flow through the media, any waste that does pass into the media will usually pass straight through or be very easily flushed when the media is maintained as part of regular filter maintenance.