With this option, you can save your current program to disk under a different file name.
When you want to make some changes to your program, but you do not want to make changes to the current version you can use the "Save As" option. It will leave your program as it was saved, and will create a new file with a new name so you end up with two copies. You then make changes to the new created file.
Note that the file is saved as an ASCII file.
File save as shortcut :