Can you solve my confusion? Some "experts" say you need to have sand

sifters like cucumbers in a Jaubert-style tank with live sand. Other

"experts" say invertebrates like that dig too deeply and wreck the water

flow to and from the plenum. Which is it?  

            What is an "expert"? We used to say "previously married" and "flow under pressure" ("ex""spurt"). But seriously; sand sifters of all sorts, fishy and non-vertebrate can be a great asset in a properly set-up and operated NNR (Natural Nitrate Reduction) system. Ideally, these arrangements have a barrier (usually fiberglass screen cloth) betwixt layers of calcium carbonate based substrate that restricts would-be diggers to the upper half. So, in my opinion, there are sufficient benefits to utilizing sifters and diggers (prevention of clogging and channeling, enhanced solubility, more stable pH, trace levels...). I'd use them; with the proscribed  permeable barrier. 

Cheesy Illustration of NNR w/Mesh-Cloth Barrier:  

--------------------------------------------------------------------      Top Gravel Layer (1-2" live sand, aragonite)

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx      Screen Barrier/Mesh

___________________________________________________      Bottom Gravel Layer (1-2" crushed coral)

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX       Plenum space and Supports under Grid/Screen