Just remember, the OS will move as it always does so the target area changes as you move the cursor, the only difference is that your tool is working up and down while your target at the OS is working side to side.
An example of when I occasionally need to use the rotation feature is if I have a photo with a blown- out, featureless area of skin (say, the reflection on a bald guy's head) and I want to steal some skin texture from somewhere else on the face to fill in the missing texture. The texture on each part of someone's skin always has a prefered direction, shadows in the pores come from a certain direction, etc., so to match up to what the direction would be in the target area, I will sometimes use the clone rotate feature.
The one thing I would add is that when I'm cloning in skin texture, hair, or anything else that should be quasi-random, I set each of the 4 clone source presets to slightly different angular values and randomly go between them to easily fudge the necessary randomness. It's a lot easier to do this on the fly than rotate one or more whole layers and then mask them out.
Many thanks Mr Sam for your kindness in helping me. You have solved my problem wonderfully, particularly as the illustrations are very clear and they explain quite lucidly how the rotation of the clone stamp tool works.
In error, I have just thanked Mr Tom, as I mistakenly thought your communication came from him. He has kindly pointed out my mistake.
Mr Tom, like you, has been very helpful, too.
I admire you both for your patience with the slow learner that I am at age 77...!