How to make required fields for some plans and not for others

I am still not understanding Fields Tabs Protect.

I have a field that is only visible for 2 plans (registration and online profile) but when I go in the back end, the field is still shown in other users who have different plans. That means, when I try and edit someone who is not part of those plans, it is forcing me to fill out that field (even though it doesn't pertain to them). Help!

CBSubs Fields Tabs Protection doesn't block fields/tabs from backend. Backend is for management purpose so blocking fields or tabs during management is a bad idea. It protects the fields/tabs on frontend. If you don't want to complete those fields during backend management then turn off backend validation within CB > Configuration > User Profile by setting "Fields Validation in User Management" to "No".

Oh does that setting just make all fields not required then in the back end?

Yes except for the core fields required by Joomla.