Billing for multiple groups
Single Group Subscription
With a Single Group subscription, all groups billed separately. If the same person appears in more than one group you will have to pay for them in each group they appear in.
Multiple Single Group subscriptions will be combined into a single invoice so there will be just one payment.
With an Organization subscription for your groups, you pay just once per member regardless of how many groups they are in.
It usually becomes more economical to switch to an Organization subscription once you have 5 or 6+ groups with some overlap of members between them.