But what if I'm changing the primary group of moderators/admins? I'm not keeping them in the registered group as their primary. Moderators have a different group as their primary and administrators have a different group as primary. Will it be ok in that case?
Me = Admin = Primary group "Admin"
Normal member = Primary Group "Member (or called registered w/e)"
Moderator = Primary Group "Moderator"
As long as none of the user groups they are part of is set to never then you could effectively do that... though you may as well just tick private node and allow access to the groups, it's a much easier and safer method.
That's not the recommended way of configuring the members and user groups, but you can do it like that.
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.
Ah, but I'm using that only for Admins and Moderators. All other members will have registered as their primary group (i'll maybe change that when the auto promote feature comes out...or maybe see how that works then decide).
I find it easier if Admins and Moderators are in their own primary group. Unless it doesn't create a problem as you said I can do it like that so I'll stick to keeping only these two groups in their different primary group ^^