Yes, yes, I know about the duplicator. However, it is only temporary. This idea would be a permanent save. It would allow you to take a small build, such as one built on a single baseplate (like what you would use the duplicator on) and save it for later use. You could in this way continue single structure builds from one server to another.
This arose from another idea of mine: modular buildings. The idea was to make buildings out of pre-conceived mini structures with set schematics that would then fit neatly together in a modular fashion. However, this doesn't help at all if these modules can only be duplicated after making them. The Saver would allow me to make these modules and then assemble them in-game without having to remake and duplicate them.
In summary, the saver would be much like the duplicator, but used for longer term purposes. This would allow something you made in another server (Say, a tower you make in every fortwars you join) to be recreated easily without going through the effort of making something you've made a hundred times before.