I wasn't in the pond when this thread started, so I've enjoyed reading it. I can't believe I read the whole thing! I have never felt a great need to be able to "read" music, but one of the things that I'm glad that I did learn is how chords are made up... major, minor, 7th, diminished, etc. I've found that little bit of knowledge to be of enormous help in working out harmonies in my gospel group. When I hear someone singing a sour note, I can play the chord and show them the notes it's made up of. If their note isn't in there, I ask them to pick one that is. Or, I'll play the chord with the note that they're singing added and they realize that it doesn't work. I would never apply the term "harmonic theory" to my knowledge, because it is very basic and I have no desire to learn more "modern" chords.

Now, if the thread was titled: understanding chords - advantage or disadvantage, the answer would be very simple... Unless you sing unaccompanied and never do a song with a chorus.. :-)

Jerry