Taz:
Bish is talking about an established, semi-stabilized reef tank (did I get that right, o Mighty Moderator?). All aquariums are attempts at modelling what is in nature, yes? Problems arise when we scale something as big and complex as nature down to a 50 gallon tank: a lot of vital pieces to the puzzle get left out. Waste that would normally get eaten or converted, isn't.
A skimmer is an export machine, designed to take a good part of what might decay in the aquarium OUT. Unfortunately, some of that stuff taken out can be useful to certain organisms in the tank. This suppresses the populations of those organisms, and suppresses diversity and complexity.
Food and chemical interrelationships can be and should be complex. We know nature is relatively balanced; for lack of completeness, our reef tanks simply aren't.
That is why we need to import (by feeding, adding calcium, fresh water, etc.) and that is why we may need to export (filtering, skimming, etc.)
A skimmer can allow you to maintain a very nutrient-poor environment, the sort that is supposedly native to many corals. A nutrient-poor environment holds fewer nasty surprises (less to go foul), in theory.
It's cheap to make a homemade skimmer, and easy to dismantle if the results aren't to your liking. Even a tank like Bishop's may not be immune to an emergency that requires fast, efficient removal of dissolved, fouling material, and that alone is reason enough to own a skimmer.
If you have an overflow-fed sump, I gave Larry M. a diagram and instructions for making a skimmer that may be applicable to your set-up. It is NOT as (over?)efficient as a commercially-made one, and you may need to read-up/ask-around some, to understand how the depicted skimmer should be placed and used.
Again, don't hesitate to ask me, Bishop (hehe), or any other members of this fine board for any help. I think that's what we're here for.
...or was it the free anemone-fritters and beer every Saturday?