Use of chords

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Just wondering if there are any threads on what specific chords are used for.  I know the dom.7 usually goes back to the 1 but what about all the other chords.  What made me curious was in mozart's vienniese sonatinas he uses a lot of 6th intervals in one of them, I forget which one.  It kept bugging me as to why he would choose a 6th interval over others.  So I was just wondering if this has been brought up as to what certain chords or intervals might be used for.