My concrete answer is "take pictures which are in focus". I used to have a compact digital camera, with autofocus, and no way to focus manually. Fine for typical snapshots. But show it a complex, interesting scene with some depth, and it would just focus on the wrong thing. It was frustrating to be able to see something, but not photograph it! Then i bought a fancier camera, which had optional manual focus, and now i could take a whole set of pictures i couldn't have taken before.