I can't say if it is common. It is a method I noticed was used more often on members who are not baptized and are "falling away from the truth". My ex-wife was one such example. I had surmised that the reason it is used more often with unbaptised persons is probably from a statistical point of view they tended to "fall away form the truth" more often or more easily then baptised persons.
One other thing I noticed is that anytime an individual who Disfellowshipped (an ousting punishment given to baptised persons) or Disassociated (an ousting punishment given to unbaptised persons) came to a meeting (with permission from the elders), it was usually made known to the congregants that this person was attending and would be segregated.
When a person (whether baptised or not) who was under Public Reproof it was announced to the congregants. The difference between the Reprooving and Df'ing or Da'ing is that with the two latter instances the congregants would avoid all contact. Conversation was left to the elders. With the Reprooving conversation was permitted but minimized. With the Private Reprooving the congregants would likely be unaware that the person was being punished. It was left to this individual to segregate themselves where possible unitl the elders felt they were "strong in the truth" again.
I have no idea how rare this last case is. I suspect in the case of my ex she should have been Disassociated or at least Publicly Reprooved (an embarrassment at the least in front of your peers) but she was of the "JW Aristocracy" so she was able to escape the type of punishment which would normally be applied.