i agree, this is a good discussion. I do mine not based on money but because i feel that it isnt necessary to use all that water and salt, then poor it down the drain. I just like to make sure they they are using the water to its max, "tapering off near the water change) and then change the water, i just hate the thought that im throwing down the drain a bunch of chemicals naturally and added to the water just because my levels in certain aread that i havent noticed to effect any of my corals over the past couple years just to have them at NSW levels. Even with all the polutants that can build up in the water over time, it cant be any worse than NSW with all the carbon filters, "pristine" salt, RO/DI water, etc.
But like Slandis3 mentioned, it depends on what you are using your tank for, what you are growing, etc.
I seen a chart on whats known/been testing in NSW and it seems that with our tanks we are playing too much as the "worried mother" which i dont blame people. It costs some good money for what people have and would hate to see them loose something because of carelessness or whatever the case may be.
The one concern that i have had, is with us dumping the water down the drain or into the ground, is what kind of impact does that have on the environment. I dont think that it's much, if at all, but still something i wonder about with a report i read a few years ago about the salt content in our freshwater supplies rising.
Which is one reason that i liked the fact that the skrubber took care of a lot of the nutrient issues with A-N-N-P and much more, and I'm not sure of what all it helps take care of except for those which have been proven on several websites, and my tank alone can contest to that.