Live rock on eggcrate, sand or on bottom?

[Reef Pilot]

I will be setting up a new tank downstairs, and resetting my current one upstairs. I have seen several different ways that people have set up their live rock, and need to decide how to do mine.

Some are setting it on eggcrate on the bottom glass. What's the reasoning behind this? Is it just to keep it from sliding around on the bottom and not scratching the glass or acrylic? My concern would be that detritus would get trapped there and collect nitrate and phosphates.

And some have just set the live rock on some sand, and some right on the bottom.

My current tank has about 3 inches of coarse sand (sort of like crushed coral and rubble). I have trouble keeping my nitrates low in this tank now, and I think it is because the of the sand. I vacuum what I can, and a lot of crap comes out of it. But much of the sand is under the live rock and at the back where I can't get at it, so I am sure it must be very full of detritus.

So with my new tank and with resetting my old one, I would like to use the same sand, but a lot less of it, just enough to cover the bottom. I would prefer to just set the live rock on the tank bottom, and work the sand around it.

Any comments and opinions about this?