I might have it muddled - I am sure someone will correct me. A scope has a set of lenses that bring the target image to your eye. Some of those same lenses bring the image of the reticle to your eye. There is actually only one focused alignment that places reticle image directly over top of target image. Set scoped rifle on sandbags - aim at target - now move head slightly left to right or up and down - if there is "parallax error" the cross hairs will appear to move on the target. So if you have different grip, hold rifle different from shot to shot - you might have barrel pointed slightly different place, even though cross hairs appear to be on the target. So, if you have very repeatable positioning - eye in exactly same place each time, parallax error not an issue for you.
I have a number of older Leupold scopes here - except for the M8-12x, I do not think hardly any have parallax adjustments. I have a few Leupold rimfire scopes that do NOT have parallax adjustment - one does, most of them do not. The books says they are set to be error free at 60 yards. Set on sandbags in my shop and aim at knot in tree outside about 20 yards away - by moving my eye fully to right side - so I start to see some black in the eyepiece, and then moving my eye to left side same way, I can move those cross hairs off that knot (maybe size of red squirrel head) each way. At 100 yard target - my eyes are just no longer good enough to see if the cross hairs move on that target. I also notice on the scopes here that do have parallax adjustment - very large distance to move objective to go from 10 meters to 25 meters - about nothing to move to change from 500 m to infinity - so I take from those two things that parallax error is going to be much worse at a close target than for a far one - think like centerfire scope with fixed parallax at 150 yards, used on a rimfire at 20 yards.