License Recycling in Multiple Communities
Communities licenses are associated with users, not a specific community. If you have unused licenses, you can assign them to users in any community in your org.
A user’s exact access depends on what the license allows, and not the community they are in.
In addition to supporting communities licenses, Communities supports all internal and portal licenses, including existing Customer Portal, Authenticated Website, and partner portal licenses.
Check out Communities and Community Users in Your Salesforce Org (external), a quick video about how communities live in an org, the differences between community licenses, and how Salesforce accounts and community users are associated with one another.