I was particularly thinking of an improper cast, yes, but the other depends on the specific choreography, partner, music, speed, and line spacing.  Sometimes it works just fine, as you say, but the floor pattern isn't as elegant and the relative speed can be all wrong for the dance narrative.   If you are swinging to improper and then are supposed to cast down, however, that's simply not possible from a standard ballroom swing; the best you can do is end the swing facing down and step apart to go down the outside.  Then the dance loses its visual structure because there's no actual cast.

It also doesn't work well if you are supposed to cross and cast--the timing changes because you are already close together, plus you need to disentangle.

I may have a somewhat unusual way of enjoying and assessing the flow of dances, because I always envision them from above as I dance.  I'll tolerate somewhat non-flowing choreography so long as the visual pattern created is crisp and elegant.  On the other hand, dances that don't create a distinctive and pretty floor pattern irk me greatly if the sequence isn't 100% natural.  (This includes just about every dance that needs the phrase "ooze" or "shift" to describe the progression. Circling to a slide, or promenading, or similar things are fine; "oozing" makes me think of radioactive sludge!)

Neal