Freezing a user versus deactivation
Key Takeaway
You cannot delete a Salesforce user. Freezing blocks logins right away but does not free up the user's license. Deactivating removes login access and frees the license for reuse.
When someone leaves, you deactivate their user, which keeps their records and history so you can hand that work to someone else. Sometimes Salesforce blocks deactivation, so you freeze the user first to stop logins right away, clean up what is blocking you, and then deactivate.
Why you deactivate instead of delete
Salesforce lets you deactivate users but not delete them outright, because deleting a user could leave orphaned records and lose critical business information. Deactivating keeps all historical activity and records, which makes it easy to transfer ownership to other users.