Here's what I do.

I copy the photos to my computer - then I copy them to the EHD and onto a CD/DVD. Then I made sure they are there - on my EHD and on my DVD

Then - and only then - do I delete them from my card.

(Paranoid much? Yep. I have too many brain glitches lately - so I need this redundancy.)

Now, when I edit - it doesn't much matter what I do to the photo - I have the extra copies to fall back on.

But, still, I edit on a copy and save with a new name. I never save over the original.