Is there a way to add a SAVE button to the main toolbar? I used the edit toolbar function to add CUT & PASTE, but there didn’t appear to be an option to add SAVE.
Ordinarily, the Save feature is just there for the psychological boost. 
Often it does nothing at all. Scrivener automatically saves as you work; more specifically it will save whenever you pause for two seconds, which for most people is quite constantly. If you’ve adjusted auto-save to a longer interval though (sometimes this is useful if you are working off of a slow device, like a Flash drive, or a networked file server), then Save becomes necessary and handy. Do note you can use Ctrl-S to save; you don’t have to use the menu.