http://reefkeeping.com/issues/2005-10/rhf/index.php
This is a great article that proves sphelps point for doing water changes.
I agree to doing them if you need nitrate reduction, add in "extra" elements to your tank through dosing, or need to replenish mag/calc/alk.
I run biopellets/large refugium that keeps my nitrates at 0, I don't dose(Calcium Reactor), so the only "extras" I'm adding to my tank are through the food I feed my fish, or trace elements that make it past my RODI(should be 0). So in an ideal world, there's no reason for me to do them weekly/bi weekly. I've been doing them recently since my tank's been recovering from the epidemic "Kent Carbon '12", just because of the excess die off that's been happening my ecosystem cannot keep up, so I've had to intervene. But generally, I've had best results letting everything stay balanced, whatever my coral takes up in elements, my calcium reactor adds. Whatever waste is produced, my bacteria/refugium/skimmer take up. Every time I did a 10% water change, my coral would lose color for a week. Now that my tank's back to going better I'll be changing from 10% weekly back down to 10% monthly over the next while, so that I can try to get the color back into my coral's since they're back to growing again.