It's a system thinking heuristic. The reason "purpose" is used instead of result is a) "the result of a system is what it does" doesn't actually make sense, as systems aren't events in time but, well, systems which have non-negligible timespans -- it sounds something like "what is the result of a dishwasher" -- I dunno, what is it doing? Is it standing there? Short-circuiting and on fire? Washing dishes? All that is part of what "a dishwasher" is, does, and therefore, its purpose in the grand scheme of things. And b) precisely to stop people trying to find purpose in motives, intentions, etc, to go with a materialistic instead of idealist interpretation of things. To quote Beer: "There is no point in claiming that the purpose of a system is to do what it constantly fails to do." The purpose of prisons is to rehabilitate? Well maybe in some countries, in other countries no matter what the stated intent is their purpose is to be a place where people can get degrees in how to do crime.