I could see the use for these being a company which needs more processing power (one MSDN blog post from two years ago talked about anywhere from 400 to 2600 servers in a standard shipping container) but doesn't have the space in their existing server room.

Also handy for temporary "pop-up" sites, maybe your building burned to the ground and you didn't have a backup site, so you're renting space and put one of these in.