This option gives you the oppertunity to create an unique copy of your diagram. This option is made make a new diagram on the basis of an old one. Normally your diagramm gets a GUIT-Number when you create it. This number stays the same all the time you work on it. Even if you change something or change the name before saving it, the number will stay the same. So when you take your basis diagram and change it and even change the name it will still have the same GUIT number and when u save it will oversave your old version. Here can you help yourself with this option. Create an unique copy copies all of your diagram and changes its GUIT number. So its possible to save it in the repository without loosing the old version of it.