CAD tip # 11170:

 You are working on a drawing and you want to make a copy of it from time to time just for the case?

1. You will use SAVE AS. But - the drawing is saved, however you are switched to the new copy. As you obviously want to keep it unchanged, you will need to switch back to your original drawing. Unneccessary steps - use another, expert workflow.
2. Type the command SAVE on the command line. This will invoke a dialog prompting you to enter the filename. Name your backup drawing - e.g. MyDrawing-copy12.dwg and save it. Now you have a safely stored copy with the current state of your drawing and you can immediately continue editing your original drawing. No need to switch drawings.

You cannot use this workflow in AutoCAD LT - its SAVE commands behaves the same as QSAVE, not prompting for the filename.