You don't need to be a scope swappin' fool like me to get good use from it. When you "get a good one," how exactly do you know it's a "good one?" It helps answer those questions quickly, easily and accurately.
I guess it's the Perfectionist/Control Freak in me.
If the scope's click value is off slightly, I want to know and I want to know by exactly how much so I can compensate if I keep the scope.
If much of the available travel in the scope is "dead clicks" at the top, I want to know about it.
If the reticle has a square adjustment range or not, it's nice to know.
If the reticle doesn't return to zero precisely every time, no sense in mounting it on a rifle and wasting a bunch of ammo to find that out.
If the reticle doesn't move smoothly and proportionally with the turrets, I want to know about it.
If the reticle is canted with respect to the turrets, I want to know about it.
If the reticle is not calibrated correctly, I want to know about it.
If the reticle changes POI with power changes (SFP scopes) I want to know about it.
If the reticle moves with the parallax knob, I want to know about it.