In case you prefer not to use the auto-save feature, Blender has a quick alternative for saving your work. First save your file as you normally would. Press [F2] and give your file an unique name, for eg. "testfile.blend". Then press [Enter] twice. Now, as you continue to modify your Blend file, you can do a three key save: 1. [F2] : Opens up the 'File Save' Window, 2. [Numpad_(Plus key)] : Increments the file name by one. eg. testfile.blend becomes testfile1.blend, 3. [Numpad_(Enter key)] : Confirms the File Save. If after using this technique, you wish to revert to your previous 3 key saved file, just press [F1] (File Open) and press [Numpad_(Enter key)] to load your previous work. In fact, you can use the [Numpad_(Plus key)] and [Numpad_(Minus key)] to toggle between all the previously saved numbered versions until you find the one you want.