Cathe really stresses posture in PH and the Slow and Heavy workouts that came out at the same time. On almost every (if not every) upper body exercise, she cues us to retract our shoulders. She doesn't do it as much in most other workouts, for some reason.
IMO, retracting the shoulder is a good idea for most upper body exercises, as it helps keep the shoulder in a more protected position in its socket to avoid impingement (at least that's what I've found for me, especially with overhead presses and chest work).
For kickbacks, always try to keep the shoulder back and down (retracted). For rows, there are various ways of doing them. Keeping the shoulder retracted isolates the lat muscle a bit more, but allowing the shoulder to go down on the downward movement, then beginning the upward movement by retracting the shoulder can involve more muscles groups (a bit more rear lat and rhomboids) and is a bit more dynamic. The less-strict form also allows you to lift heavier. Either way works, and IMO it's good to vary.
Whatever form you use, make sure you are always in control of it, and are doing it for a reason (rather than just letting your shoulder "kinda hang") and you'll get more out of it.
HTH!
