While the parallax knob is often used to 'focus' the target at different distances. That is not the actual purpose of the function, and is actually an incorrect use for it. The parallax adjustment is meant to put the optics in the same plane as the target. Which in turn makes your sight picture parallax free.
In the beginning rifle scopes had adjustable objectives that would focus the target image on the scope's reticule; exactly like a camera lens focuses the subject on the film. If the target image ain't focused on the reticule, it will appear to move around the reticule as the aiming eye moves around behind the scope's eyepiece. Such condition's been called parallax since rifle scopes were invented in the very late 1800's. And everything in the view of the scope will not be parallax free; only things at the range the scope's focused for.
More recently, with so many rifle shooters not understanding basic optical lens functions in telescopes, they started calling the process of adjusting the objective lens to focus on target "parallax correcting" and in order to make more sales of rifle scopes, many makers as well as dealers began calling that functional part of the scope a "parallax adjustment."
That aside, the scope only focuses things at one distance sharply on the reticule. Everything closer is focused behind the reticule (closer to the aiming eye), everything further away is focused in front of the reticule. As long as the aiming eye's kept on the optical axis of the scope, there will never be any parallax of the reticule on the target's aiming point regardless of where the objective (front) lens group's focused. That's when the aiming point on the target, the focused target image on the reticule and the aiming eye are all exactly in line with each other.