User license assignment and recovery
Key Takeaway
You can't delete users, so to free a user license for someone else, deactivate the user. Freezing a user blocks login but doesn't free the license.
Every Salesforce user needs a user license to access Salesforce. The license sets the baseline of features and data that the person can reach. Admins assign a license when they create a user, and they can change it later by editing the user. Because users can't be deleted, deactivating a user is the way to get a license back.
What a user license controls
Each user can have only one user license. Choose the license type based on the person's job functions and the permissions they need for their day-to-day tasks.
The user license is only the baseline. You can turn on more functionality with permission set licenses, or by buying feature licenses or usage-based entitlements.
Profiles and user permissions then adjust access within that baseline. For example, they can let some users only read records, while other users can also create and delete records.