Remove User on Remove, or Purge?

[ms419]

If a package creates a user when it is installed, should it remove this 
user when it is removed, on only when it is purged?

I couldn't find this topic in either the Policy Manual or Developers 
Reference.

I did find some interesting information about packages creating & 
removing users, but it doesn't exactly answer my question: 
http://lists.debian.org/debian-mentors/2002/06/msg00208.html

Thanks!

Jack