If you're the "better safe than sorry" type about losing your files, you might be using cloud synchronizing to have your files automatically saved in case some disaster happens to your computer, leaving it utterly destroyed forever.
My choice for this purpose was Google Drive and so I recently transfered all my files to it, and kept on working from those that automatically synchronize online. Very convenient for a scatterbrain like me who can hardly follow a back-up routine.

However,I noticed that sometimes, while saving a Photoshop file (rewritting the same with newer, current version), I would get an error message telling that the file couldn't be written due to "name error". So I'd just save as with a slightly different name.
Yesterday I was lazy when I got the same error for a file I had hardly altered (just changed the visibility of some layers), and I didn't save as. Now that was a big mistake, because what happens when you save a file, is that it gets deleted and then written again. And when you get this error message, the file is already deleted, so saving as is your only option to keep your work from being erased.

Don't be lazy or you will cry ;n;