> Where did you guys get that idea that prescription should match so very precisely?
It's often much less about the prescription than the characteristics of the material used for the contact lenses and the measurements of your eye. The base curve and diameter portions of the prescription are used to capture this.
> Why do you need a specially trained person to dispense a box of contact lenses?
There are two reasons. With the wrong set of contact lenses (e.g. off-prescription color contact lenses that people wear on Halloween), you can significantly harm your eyes due to low oxygen permeability in the lenses, lack of fit, etc. Second, the contact lens/glasses prescription renewal process forces people to get an eye checkup done, which can often allow the doctor to identify other problems (e.g. infection, cataract, etc.)
It's subjective whether or not using this as a forcing function is really the "right" thing to do, but it does prevent people from living with undiagnosed issues.
> Also, what's the deal with vision insurance?
As people get older, the likelihood of an eye issue increases dramatically. This depends on your specific policy and what it covers, but there are "insurable" (i.e. low likelihood of occurrence, very high cost) events that can occur with your eyes that your VSP policy may cover. I'm not deeply familiar with this, so I can't comment extensively on it.
