Sand bed ---> bare bottom

[Richer]

Pros:

You have the ability not only to increase the flow rate of your tank, but to distribute it evenly all over your tank... rather than having a large majority of it directed in the top half of your tank. Many SPS keepers are a big fan of big flow rates. Its easier to keep a tank clean with a BB because detrius does not have the opportunity to build up in a sand bed, and higher flowrates can keep them suspended in the water column longer, making it easier for your overflow+sump or any mechanical filters to remove it from the main system. Having no sand bed also gives you that extra couple of inches of space that is normally occupied by the sand.

Cons:

Certain kinds of fish (ie. sleeper gobies, jawfish, etc.), corals, etc. cannot be kept without a sandbed. Quite a few people don't like the look of a BB tank.

-Rich