FWIW, some of what people claim in that linked discussion is not true.
Summarizing what is true,
1. Regardless of what bioballs do, if you have adequate nitrate export, you will not have a nitrate problem with or without them, and with inadequate export, you may have a problem with or without them.
2. There are two reason bioballs are a nitrate "factory":
A. One is that detritus can collect. But that only matters if the detritus is somehow otherwise removed from the tank. If it just settles elsewhere, then that isn't a factor.
B. The other reason as to do with where nitrification and denitrification take place.
I discuss (B) in this article:
http://www.advancedaquarist.com/2003/8/chemistry
from it in the section on how to reduce nitrate:
Remove Existing Filters Designed To Facilitate The Nitrogen Cycle.
Such filters do a fine job of processing ammonia to nitrite to nitrate, but do nothing with the nitrate. It is often non-intuitive to many aquarists, but removing such a filter altogether may actually help reduce nitrate. So slowly removing them and allowing more of the nitrogen processing to take place on and in the live rock and sand can be beneficial.
It is not that any less nitrate is produced when such a filter is removed, it is a question of what happens to the nitrate after it is produced.
When it is produced on the surface of media such as bioballs, it mixes into the entire water column, and then has to find its way, by diffusion, to the places where it may be reduced (inside of live rock and sand, for instance).
If it is produced on the surface of live rock or sand, then the local concentration of nitrate is higher there than in the first case above, and it is more likely to diffuse into the rock and sand to be reduced to N2.
