That is the setting range you want to be in, or, what I would want to be in. I wouldn't even suggest that there is some law that requires those settings. They are the values that through experience I have come to start with. I numbered them like that as when I do it, I don't actively think. Most is an automatic response of knowing what the reaction to an adjustment will be for me.
Most people think of the three legs or variables when posing an indoor shoot. They are aperture, shutter speed and ISO. Those are all fine and dandy, except, especially indoors, we can add a diffent variable in the amount of light we use. By adjusting the artificial light (strobes, flash, flood, etc) we can keep the subject reasonably lit without over or under exposing. At the same time, you also want some depth of field and avoid movement blur.
I will generally use Av priority so if there is some adjutment in light values, the camera will compensate automatically without the need to recheck everything. Manual would require a more complete check. I prefer Av inside as it is easier to control my DOF whereas the shutter speed is much more minor, provided there is limited movement or it is set high enough. And do do a camera lighting check. If the Av is set, you can still vary the ISO and / or the light in order to reach a desired shutter speed.
When all the variables are known and stable, we can predict the result with more accuracy. Like a school photographer, he sets up once, takes a test shot and once happy, will shoot from a few hundred to a couple thousand shots, without any adjustment, by using the same pose for everyone.
Don't think of adjusting your ISO as the limit in lighting. Even shooting outdoors I will occasionally use reflective panels to increase my subject light. The important part is what values you set the camera to in order to get the desired shot.
