I keep all my edited images in their full-layered states in the event I want to go back and play around and/or re-edit an image.
Problem is that my file names are usually DSC_XXXX.
Recently I've been encountering the following error message:
Thinking Photoshop was lying to me, I have been saving anyway. Little did I know that I was overwriting existing files. My rationale was, "That's impossible, I just shot this. How could there already be a file with that name on my computer?!?"
Simple, my file names have been used and reused because it only records 4 digits (DSC_XXXX).
So I have recently changed my file name to write DSD_XXXX for new file names that won't recycle at least for a while.