said by robbin:
How exactly does the landscape fabric help with this?
As you can see in the picture of the DeltaMS, it's dimpled plastic. Once/if it gets a little bit loose and starts moving up and down when you walk over the floor, it would hit the concrete slab and do click-clack noises. The landscape fabric acts as padding so there isn't that noise.
This thread is what inspired me to do this sort of subflooring (with landscape fabric).
It's also where they discuss using DeltaMS instead of DeltaFL.
It's long but interesting.