Can't answer all the technical stuff, but yes...a fuge serves the purpose of being a place to
1. store ugly apparatus like heater and skimmer (like a sump in this way)
2. have a place to safely grow
macro algae that helps consume nutrients (this requires a lit area, not like a sump)
3. a fish free zone where pods are encouraged to grow, which eat detritus and feed the fish when they are either manually harvested or simply overflow into the main tank.
Now you may choose 1 or more of these uses. I know that some people will put damaged corals in there to keep them from being picked on by fish, inverts and other corals. You could technically give protection to a hurt fish, but it would not be a good quarantine.
WG