Based on personal experience, I have to disagree to some extent about the statement above.  While my system (120G tank / 150G volume) is not necessarily considered a large system (over 180), it has undergone quite a change over the last year.  For several years, it was just mainly a softie/LPS tank with no fuge, but last year, I decided to ramp it up.  As my sump was already full, the only way I could add a refugium was to do it remotely, in another room behind the wall.  At the time, my nitrates were testing in the 30 - 40ppm levels and, within 30 days of adding the refugium, they fell to undetectable levels.  I haven't gotten so much as even a slight tinge of pink on the Salifert test ever since, even at low range through the side.  Same goes for phosphates.  I've since taken further steps to reduce the possibilty of nitrates and phosphates creeping up by upgrading my skimmer, adding a GFO reactor, etc.  But to say that small fuges do nothing at all, at least in my experience, is certainly not the case.