As much as older-school composers (or at least, composers who came up before, say, the 90s) decry the ability to playback from notation programs, I have noticed–I guess I have always noticed this but especially recently–playback has shown me that my harmonic rhythm is usually way too fast. I don’t think this occurs to me if I am listening in my head, or even playing things through at the keyboard, (although I usually start with those processes), these problems just don’t register. But as soon as I am confronted with some semblance of what it’s like to be a listener, with the music not rhythmically not under my mind’s direct control, then I almost immediately have the sense of “whoa whoa whoa, slow down”….. . . In some cases a frenetic harmonic rhythm pace is appropriate, but in general I would like the listener to be able to experience and understand why I make certain harmonic decisions, and it is necessary to slow things down enough so that that is possible.  (And I don’t mean “understanding” in a technical sense that you could describe in words, just the feeling of the harmonic movement).  So lately I will write out a passage, and then play it back and just end up writing copious numbers of notes above almost every measure, “expand this . .expand this.. . . expand this. . . ” .