The KantanMT's REST-based API with JSON responses is designed to aid mid-sized local service providers (LSPs) in delivering KantanMT translation capabilities. KantanMT is a statistical machine translation platform (in contrast to a computer assisted translation service). The big advantage is speed: the service is available instantly, faster than you can say, "qu'est-ce que c'est?"
So, you're trying to share some files with someone who only has access to an old version of Word. Or maybe that Microsoft-hating friend of yours who only uses WordPerfect. Perhaps you want that old-school ebook to be an epub, rather than .lit. For any of these problems, there are desktop apps that work, of course. However, sometimes you want to be able to do that within a program. If so, Doxument and the beautiful Doxument API are what you need.