I have a sort of shallow bed, up to 4" in some spots where the flow is low down to 0" where the flow removed it all.
I have never had any problems that I could definitely point to the sand bed and say "you did it" and I really like the look of sand even when it won't stay where I put it
*edit* I use sugar sand now. I've tried the coarser stuff and found I had problems with detritus settling underneath, with the sugar sand the detritus is larger then the sand (for the most part) and stays on top until water flow, fish or worms clean it up