Even if it was 100% safe to do so, I figure the wear and tear on the buttons is reason enough to not do it.
I do any deleting from the computer and then only those files that I am 100% certain that I never want to see again.
SD cards are cheap, even for a pauper such as I, so we have always just used them until they were full and then archive them as another means of backup security.
When we have several SD cards that are too full to use, yet still have a GB or so of space, I use multiple card readers and transfer files from one to another until I end up with a few completely full cards and some empty ones as well.
Elements 7 ~~~ 64-bit Windows 7
On a poverty-level Kentucky budget, a 24-exposure roll of film would have two Christmases and a summer vacation on it and we might have to wait another six months before being able to afford developing the film.
I still have trouble remembering that it doesn't cost anything to take thousands of pictures; it just almost seems impossible to be true.