hey pat, not an expert at all, but from my experience a sand bed in a refuge has been great to promote micro fauna diversity. Other than that there are so many opinions out there as to the benefits of denitrification etc, but from my perspective, any 'refuge' you can provide for micro inverts is a benefit and has worked well for me. I guess it will all depend on what you are trying to keep and what kind of environment you are trying to provide. I personally like my DSB refugium with mangrove and macro, but there are lots of other opinions out there!
Hope you get lots more opinions!