It's quick, easy, and, except in cases of high IWs and HBPs, achieves the same goal of putting a measurement on a batter's plate discipline. That's why the first thing I look at for a player's is his slash line BA/OBA/SLG, because not only do each of those numbers tell you something about the hitter but so does the relationship between each of them. Walk 'Rate' is probably the wrong term for it but you find out about a hitter's walking ability just by looking at BA v OBA. Then Isolated Power (IsoP) is the gap between BA & SLG which effectively becomes a player's Slugging Average if you factor all his singles out of the equation. Any single, after all, including infield singles and bunt singles, increases one's 'Slugging' percentage which is certainly misleading at best. From 2004 to 2008, for instance, Mike Cameron (802) and Ichiro Suzuki (803) had near identical OPS, but of course were completely different hitters. Ichiro hit .332, 82 points higher than Cameron, but walked infrequently (46) and hit for little power (IsoP = 93 where 150 is around league norm) Cameron hit just .250 but walked at just about double the rate (85) and his slugging was 217 points above his BA. So a quick look at the slash lines of the two tells you a lot about what kind of hitter each is even if you never saw or heard of either of them. And there's no math involved beyond simple subtraction.