Rc27 is in my opinion the most important offensive stat in baseball. It values a player based on how he hits and puts no value on runs and RBI that come as a result of his placement in the lineup or his teammates performance. I have my own slowpitch softball team in real life. We are pretty good for a bunch of wannabe MLB hacks. We have fun and play a competitive schedule. 150 games, 10 months per year with some minor travel. This is the stat we use. We only look at OBP and Rc27. (We use Rc21 because of the 7 inning games)
Here is why Rc27 is important. Slugging percentage is not an accurate measure of the value of each hit. In other words, a homerun is not 4 times as valuable as a single, and this has been proven by statistical analysis by guys much smarter than me, like Bill James. Now the system we use was adapted for slow pitch softball but basically I value a single at 0.47 runs and a homerun at 1.40 runs. I tested on several tournaments and it would always be +/- 5% of the runs we actually scored. In other words we might score 79 runs and the formula predicted we would score 81 (for example).
It makes it much easier to see what lineup changes need to be made. Because a guy hitting 9th in baseball doesn't get as many chances to drive in runs as a guy batting 4th. A guy hitting 7th won't get as many chances to score runs as a guy hitting leadoff. Few would disagree with that. So that's why I look at RC stats instead of RBI and runs scored. RC will give a true value to a good hitter that plays for a bad offensive team. Runs and RBI never will.
RISP may be a more popular and more easily understood stat, but I don't want in included at the expense of removing RC stats.