Other than aesthetics and providing essential habitat for a very select number of organisms, sand serves no purpose that can't be accomplished another way.
I'm not sure I agree with this statement. Just because you can do things other ways doesn't necessarily mean they're as good or natural.
One of the reasons I like my sand bed is simply because of what it produces: lots of microfauna and food for organisms in my tank. Living creatures like 'pods, mysids, bristleworms, etc. serve the dual purpose of providing a natural food source/supplement while keeping the tank clean at the same time by consuming excess food and waste. Frozen or prepared foods just can't do that. I can't imagine that my current little group of baby Banggai cardinals would grow as fast as they are with NO feeding in a barebottom tank. At about 4 weeks most of them are right at an inch now. Prepared foods are just that-prepared-and generally add excess wastes into the water (ash, processing agents, etc.).
I also like my sand for the purpose of denitrification. I don't stock my sandbed with anything other than the natural tiny critters that inhabit it. There's a multitude of 'pods, snails, mini-stars, worms, etc. that inhabit my sand bed. Nothing larger that disturbs the bed any more than that. Nitrates and phopshates are at zero after two years with no water changes, so I believe it's really more than just a pretty face.
The other tidbit of information I picked up along the way, and I honestly don't recall where I read it (but it was a reliable source from what I recall, otherwise I'd have questioned it) is that most of your nitrification and denitrification takes place in
the first quarter-inch of your sand bed. Which is one reason why I don't run a deep sand bed any more. Grain size on play sand is perfect, it's cheap, it doesn't compact like aragonite can, and it's served me well for nearly 6 years now in various tanks.
If you like doing constant maintenance, lots of water changes, testing, etc etc., then more power to you. I'm lazy.