Everyone has a photographic memory,
but not everyone has film.
Screenshots are immensely useful — not only to document your work methods/settings, or to get that image in the browser that you just can’t save otherwise. I’ve used Mac’s Grab Application for ages, until I found the following keyboard shortcuts.
The advantage of these keyboard shortcuts (shift + command + 3 or shift + command + 4): The images are saved on the Desktop as png. It does not get easier than this.