Many people use sand for the bottom of aquariums, its cheap, easy to maintain, and looks good.
Pros of sand:
Cheaper than gravel if you buy the 3 dollars 50# bags.
IME, when plants root down, they can have a pretty strong hold to it.
Bottom dwellers will love you for switching to sand.
The poo stays on the surface making it easier to clean.
Cons of sand:
The poo stays on the surface makiing it unsightly.
Depending on the type of sand, you may have to spend a lot of time rinsing it.
If you don't stir it up every once in a while, bubbles of noxious gas build up under it.
In the end, I would rather use sand on my tanks than gravel.