[TheLastSuperman]

On many forums a majority of it's member base are spambots, due to a number of factors/reasons. When you have a large number of "bots" or members who have never posted you should simply move them to an inactive usergroup without posting permissions in my opinion as I see no reason to delete a spambot type of account when another registration attempt takes place.

The reason you move inactive and spambot members to a specific "junk" usergroup is to count the actual number of valid members from other usergroups who actually interact with the site IF you want to provide some form of honest credentials aside from basic site traffic stats etc.