One of the reasons that I like playing in octaves is that it makes more sense of splitting the notes of the chords over a wider range. If you play three note chords on the concertina they sound better if you spread the three notes over two octaves rather than one. This is to do with the way that the harmonics of concertina reeds can clash with harmonics from another note. It is fascinating to look at a computer screen showing just how many different harmonics are in operation from a single note. I have a friend who goes round collecting data from different concertinas as he is trying to make some scientific sense of why concertina reeds, accordion reeds and hydrid reeds act differently!