scoria is good but blocks up easy and gives about 250sqm per gallon.
Again, that is to be used in a power filter.
I guess it depends on the type of tank one has, the stocking, and what the person feels most comfortable with.
None of my tanks would survive without a cannister filter or 2 and a copious amount of media.
then again, there are those that can stock lightly, do water changes and have an undergravel or similar and be fine.
Plants and UG's dont do too well though.
Given today's busy lifestyles, where we want to spend more time appreciating tanks, than to sit maintaining them, I think cannister filters and media are a real boon to us.
I know I personally would not have any tanks if I did not have cannister filters to go with them.