There are a few good reasons that one might build with shipping containers, and probably more reasons why one shouldn't. Steve of the Tin Can Cabin blog documents his building of a three-container cabin and his conclusion that it except in certain circumstances, it in fact it doesn't make much sense at all.
Steve's reason for building with containers was simple: security. Compared to a regular cabin that might take a minute to break into, it might take 10 or 20 minutes with the right tools to get into his container cabin, and people probably won't bother. He questions all the other purported benefits, including the green recycling argument:
Nor does he see any cost savings, and has all the answers for the people who say "“I can build a container cabin for $20/sq foot” or “your cabin is overbuilt and too expensive”. Both of these comments are true if you don’t mind living in a shack more appropriate for a third world refugee camp."
Shipping containers are best used for what they were originally designed for – the shipping and storage of goods. By the time a container is no longer able to do that effectively, I’m not sure I’d want to build with it anyway. If you feel the need to reduce your environmental impact, build small and insulate well.
He then runs through the costs, and notes that even if the shipping containers are free, by the time you add shipping, crane rentals, welding and reinforcing (needed every time you take out a bit of wall) it is still going to cost more that 50 bucks per foot before you even get started with the finishing.
He touches on other issues, ranging from approvals, the toxic floors, the difficulties of wiring, trim and plumbing (compared to normal construction) and the obvious design limitations that come from the fixed container size, designed for freight and not people. He concludes:
I’m not telling anyone they shouldn’t build with shipping containers, just that they should truly assess their reasons for doing it before they proceed. A shipping container cabin can be comfortable, secure, and aesthetically pleasing, but it will cost you considerably more than a conventionally built cabin....In summary, I don’t regret my decision to build with containers. The peace of mind when I lock up my cabin is priceless – well, at least $15K worth.
Speaking from the experience of building, Steve makes many of the points that I have made in posts like Does Shipping Container Architecture Make Sense? It does, in certain circumstances. It's a fun meme that has produced some interesting architecture. But it isn't necessarily cheap, green, healthy or comfortable.