You really shouldn't be moving anyone out of the default primary usergroup which is Registered.
The system has been designed to be used that way.
There is no distinction between primary and secondary user groups.
It is recommended however that all users have the Registered user group set as their primary user group and any additional groups they are members of are set as secondary groups. This makes it easy to manage permissions due to the cumulative nature in which they are applied.
I would rather not but I need to moderate new user's posts. The site is growing and along with growth comes more spammers and troublemakers. So now I need to moderate all new accounts. Any suggestions?