The main reson I find rwKW handy is to see what differance to power your mods make. As well as an easy way to compair you car to others. Yes 1/4 mile times would be better, but personally I have taken my car to the drags and probably never will. So the only stat I have for the car is the mods and the rwKw.
The first time I put a car on the dyno was my old 260z, it had some mods from the previous owner. I did a few things to it as well. I stared with 77rwKW and ended up with 96 rwKWw. Compared to my stock R32 GTS-T doing 140 rwkw there is a big differance, but what I look at is the change after mods (ie 19kw increase).