I have to agree with Smojo about the difficulty in retrieving stuff from the bottom of barrels - above ground you can simply tip it out, but if it's buried getting stuff out of the bottom could prove downright dangerous - a while back I got trapped in a waterbutt! It was not funny.
http://gardeningboots.wordpress.com/2009/04/19/das-butt/
That is hilarious, at the time I imagine it was frustrating, but looking back you must see the funny side....