There are situations where Shot Match will not work, particularly if the shot is substantially different from the shot to which you're trying to match. Pages 664-667 in the manual cover it pretty well.
There are also a lot of artistic considerations involved where a perfect technical match doesn't necessarily compensate for the lighting or angle involved. For this reason, colorists often have to use secondaries, windows, curves, and keys to get the two shots in the same general area.
Shot Match can work (though I've never used it) if you have two identical shots shot in the same place with the same person, only in one the lighting has changed. In theory, Shot Match could get you in the ballpark, but it won't get you all the way. I find it faster just to turn the knobs, use the scopes, and use my eyes, comparing a reference still. Time and experience will eventually make the process go faster, but some situations are always open to interpretation and nuance.