Aloha,
It's mostly about personal preference, what looks good to the hobbyist.
I
have found that a 1" layer of Oolitic on the bottom with a half inch of
larger particle sand of your choosing works very well. Less Oolitic
sand is required to do the same job as larger particle sand. With a sand
bad that is only 1.5" deep, there is more room for coral and fish.

Oolitic
sand is not so difficult as you would think. It requires water flow
which also improves pH and after 2-4 weeks the life living in and on the
Oolitic sand holds it together. The tank below was practically all Oolitic sand.
Using just a cup of LS from an established reef tank is 10x better than buying the Arag-Alive live sand.
The link below, WMAS Reefkeeping Tips, tells more about it.
Mahalo,
Mark
