If you don't have algae (or unusually high chlorine demand or water turning dull or cloudy) and you have <= 0.5 ppm CC, then you don't need to shock. Even if you have some CC that's a little above 0.5 ppm, you could wait a while and see if a sunny day plus some time takes care of it. Usually this would happen after a heavier bather load -- you could shock if you wanted to, but could just wait a day or two instead.

Sometimes if I get a suntan lotion film on the water and am impatient at getting rid of it, I'll shock or use a non-chlorine shock. I use the the latter if my wife is swimming every day and doesn't want to be in at higher chlorine levels. This situation is rare -- I've only done it once and usually I just let the film be as it does clear up if she doesn't keep adding to it every day.

Richard