Bio-balls come from the "old age theories" of keeping fresh water fish. It was indeed use in the times when reefkeepers did not keep as many corals, as in today's times. And also not as many SENSITIVE corals.
The draw back of ceramic noodles AND bio-balls, is that yes - it works to break down ammonia into nitrites and nittritest into nitrates - BUT, it is NOT conducive of breaking down nitrates into nitrogen and oxygen and hydrogen... this is where the DSB works best...... it goes all the way in the WHOLE nutrient cycle.....
In fresh water tanks, aquarists used to have many freshwater plants - which took up nitrates and phosphates.
Therefor the implementation of "algae scrubbers" in marine tanks - to take the task of fresh water plants - to "use up/export" nitrates/phosphates from the water.....