I found out the hard way it makes a big difference. Bigger than most people think. If you do the math, it can be significant, but alot of factors are involved like F factor, and focal length, distance between the lenses and more.

I had a muzzleloader scope on my muzzleloader with parallax set to 60 yards before. It shot 1" groups at 50 yards and 2.2" groups average at 100 yards.

So I had the bright idea to put a Vari X III 1.5-5X20 on it. Parallax set to 150 yards. My groups at 50 yards opened to 2.5" groups. But at 100 yards stayed at 2.2" or so. Very consistently. This gun is rock solid. But I was looking thru my scope and moving my head around, and sure enough, at 30 or so yards the POI on the target is moving around 2" or more. I put back my old junk scope back on. And everything went back normal.

I am going to chip in the 30 dollars to have the parallax set to 50 yards.