This can get you up close and personal with the tune's harmonic structure, as well as its harmonic and melodic resolution points.
It will also reveal where you are in terms of your own aural understanding in relation to where you might want to be (this never stops - it's a continuous process!).
One particular tune I personally wanted to delve deeper into was "Come Rain or Come Shine" - music and lyrics by Harold Arlen & Johnny Mercer. It debuted as part of the 1946 Broadway musical "St. Louis Woman", and has since been performed and / or recorded by just about everyone and anyone. It's enshrined as part of the "Great American Songbook".