I am using sand for the first time in my brooder, and I LOVE it! In the past, I have used pine shavings, but found it to be very messy and hard to clean. The sand is easy to clean because it has a drying effect on the poop, and as such causes it to clump...kinda like cat poo does in litter.
Also, I have not had a problem with pasty butts on any of the chicks...I think it is because they ingest some sand, and this acts as grit. Just my opinion on this from observation and research, but seems to be true.
This summer, I plan on using sand in my runs. It would drain well, and be easy to clean. Also, because I have silkies and brahmas, I think the sand will be good to use because it will prevent mud from damaging the feathers on their legs. I would only use the white play sand (limestone), not the brown. White play sand is a little bigger particle, and is not quite so dusty.
Another thing I am thinking about is using sand as a base in my coop next year. I already have all the pens set up for this winter, or I would do it now...maybe I'll work on this a little before winter REALLY hits here (Northern New York)...What I have going on now is many separate pens with breeder pairs and trios by variety and breed. My shed has a cement floor, which is cold and holds moisture. Although I have a good, deep base of pine shavings, they will dig and scratch down to the cement. I think I will put enough sand in to make a 4 to 6" base, then add shavings on top. I can still clean out the shavings as needed, but still have a good base with the sand to insulate from the cold, damp cement. I mostly like the shavings for the insulating effect from the cold, as they can hunker down and fluff up in them when it gets really cold. I'll see how it goes with the sand, and report back. I might try this idea out this weekend in two of my pens if I can find some white play sand.
From researching this topic, I believe that sand is the way to go for many reasons. Perhaps the only downside would be the dust factor, but you will get that with any type of bedding/flooring.
Just my opinion...