Effects of deactivating a user
Key Takeaway
You can't delete a user in Salesforce; you can only deactivate them. Deactivation removes login access, but the user keeps their records until you transfer ownership.
Deactivating a user is how you offboard someone. It turns off their ability to log in to Salesforce while keeping their records and history in place. Deactivation affects licenses, sharing and teams. It also affects Chatter, automation and reports, so you need to know its side effects to plan the cleanup.
Why you deactivate instead of delete
Salesforce doesn't let you delete users, because deleting could leave orphaned records and lose critical business information. Deactivation keeps all historical activity and records, so ownership is easy to transfer later.
A deactivated user stays in the list of users, shown as not active, and you can still see their name on the Users page. Deactivated users can also still appear in Created By fields.