One must ask, why do we do water changes? My understanding is to reach a balance of import and export of good vs bad disolved matter. I find this is a hotly debated topic with the reefers where this is probably more crucial. And... they cannot agree.
I find this topic of water quality a facinating topic and there is tons of info on this out there.
What the folks are saying above is, that it depends on your individual tank. Assuming your bacterial/algae balance is good, all you probably have to worry about is the build up of nitrates. So do your water changes to keep them at an acceptable level.
As you can see, there is no real agreement on this either!
So... read as much as you can and decide for yourself on what's best for your tank.
BTW, I have a heavily stocked african tank and only do about 30% monthly.
Hope this helps????
mark