In time and motion ungainly movements are ugly. Little things altered do enhance pleasure.
This first exercise is so big it will take you years to understand it. How many progressions can be developed above a single root? Four instruments play together, each given a different note on a different stave, so we hear a progression of 4 note chords. With bass accompaniment these four note chords can be extended by a single C root/bass.
For the first chord change every note drops a semitone. For the last chord change there is a wonderful subtlety in two notes dropping a semitone and two notes staying as they are.
We needed one line ascending and another descending from Bb to G. When we altered the Bb chord to Bb+ we were able to ascend and descend chromatically.
Similarly the progression from Bb7 to Eb6 is made much more subtle and interesting by Bb7+. Then two notes ascend chromatically and two notes stay as they are. F# to G compliments D to Eb.