Chem_geek really, really likes precision. In some of his pool work, those determinations matter when you are attempting (as he is) to understand what's happening with the pool chemistry, at an analytical level. But you are right that 0.2 ppm chlorine rarely matters for most pool operators. However as he also notes (more importantly) DPD-FAS allows measurement of high levels of chlorine.

Generally, you can't manage chlorine at high CYA levels, not because of 0.2 ppm differences, but because of 10 ppm differences. Only the DPD-FAS kits allow reliable distinction between 10 ppm and 25 ppm FC.

Or, if you mess around with copper (ionizers, "minerals", etc.), 400 ppb Cu may not stain; 600 ppb probably will. Target levels are often in the 300 - 500 ppb range (0.3 - 0.5 ppm).

Ben