RBass is good for kick drums in my opinion. All the other stuff gets farty in the low end. (As a track insert!)
However, I used it once for mastering, because the original kick was dull, lacked sub bass but had tons of upper bass. So I C4'd the upper lows and then hipassed the mix at 60hz, with a moderate slope, then I slapped RBass on it, set it to 32Hz and moved on with the dynamics of the whole track. The result was punchy, clear and even lowend.
That's one of the specific uses that you can give it, although I wouldn't consider it an usual mastering plugin.