My personal opinion is...it doesn't really matter.
I don't
like deep sandbeds because of the
potential issues that
could be associated with it. I like to avoid potential issues whenever possible. Having no sand could have potential stock selection issues. So, that means the happy medium is
some sand...?
My 90 started off with 4" deep sand on each end for Jawfish paradise, and then 1" in the middle because I didn't want too much sand. This was all fine and dandy, and the Jawfish kept the sand clean. I eventually siphoned out most of the sand so there was a little less than an inch all around. The Jawfish is now no longer, and the tank got dirty (long story you've probably heard before) so I siphoned the sandbed out. I couldn't be happier. My tank just has a light skiff in some places, but mostly bare. Coralline algae is starting to cover the glass and I really like the look. The color of the coralline is whitish/pinkish so it doesn't look much different than sand, but without the mess. I like that detritus is easily siphoned out during waterchanges.
Keep in mind I'm a sand vacuumer. I vacuum it right down to the glass all over the tank on every waterchange. I wouldn't do it any other way. I also don't notice any detrimental effects to the sand inhabitants. Well, that was when I had sand.
I have a wrasse and he just lays on his side on the glass at night...he doesn't seem to care, and I get a chuckle out of it. I did have a pile of sand in the back for him, but he didn't use it, so I siphoned it out.