DD used to have what most called a long finish, with right hand leaving the bat and left hand carrying it around. That stopped after a shoulder subluxation (partial dislocation). She now finishes with both hands. Has more power now.
I have heard D1 hitting instructors say it does not matter so much, as long as it follows extension. For younger players, I have noticed that release of the bat is more typically the result of some other failure in their mechanics. So, I will usually correct them unless it was obviously not driven by poor mechanics.