Deep sand bed

[MitchM]

It depends on what you consider beneficial.

You could either have a display sand bed that needs to be cleaned regularly.
That way you could have any grain size you want, any depth you want and keep any animals you would like.
That kind of sand bed needs to be cleaned by you.

You could have a properly set up and functioning sand bed, intended to process any detritus that falls on it. (within limits!) A heavy bio load can overwhelm it.
That way you need specific grain size, at least 4 inches in depth, no crabs, shrimp, sandsifting gobies, sand dollars, sand sifting starfish or any other animals that sift or move sand. They will essentially eat all the bethnic infauna that keep the sand moving properly.

Either sand bed will still help with denitrification.