Depends on the situation and what you like personally. My present 100G is 9 years old with a 330lb. 5-6" Southdown DSB and I would not have it any other way. I have had bare bottom, crushed coral, shallow decorative sand and everything in between and will always go DSB in a larger system. In a small system you may not have the surface area of tank depth for a DSB and in that case I wouls stick with 1" or less and vacuum it. The DSB gets no maintenance or cleaning and is hard for some who like to mess with things a lot and disturb the anoxic and anerobic bacterias and kill the system. The key is good circulation and leave it alone.