What? Doesn't 20/20, 20/15 etc. refer to visual acuity (how much detail you can see from a certain distance)? Are there people who prefer anything but the highest possible visual acuity?

This I think has a lot to do with individual experiences with optometrists. I went to probably half a dozen optometrists since adolescence before I happened to end up with one who actually made it clear there's a degree of subjectivity with an eyeglass prescription.