....Silly question, maybe, but I couldn't get any related info:
What is the difference between checking and non-checking the "Save as new document" box?
When should I choose the first option and when the other?.......
Search the forum about the UUID - universal unique identifier. When you 'Save as new document' the file is saved with a new UUID. Clearing that check box will do a regular Save (or Save-As) without creating a new UUID.
Sometimes that's correct, like when you are using one file to start off a new design for another file. Sometimes that's not a good idea, because the previous linked drawing file will no longer link to the new file.