Following is a faithful recreation of some advice offered by a self-described professional photographer:
Do not delete files from your digital camera as you go. Download all of your images onto your computer and delete from there. When you delete files from the camera individually, you get rid of the pictures you don't like and you make more space on your card. But in doing this, you also "make space fragmented on the card." There are "little sections of space" remaining where you deleted a photo, and the card tries to fill in those spaces. This can cause card corruption.
So, is that sound advice, or is it just another of the 82,433,516 irksome, niggling, persnickety warnings of disaster that, if heeded, will turn photographic fun into a fathomless morass of anxiety and dread?