Sometimes, someone that once needed to access the Resource Planning tool, doesn't need it anymore. That's why you can delete Users. But remember! Users aren't Resources. If that someone had a Resource, you'll probably need to delete or archive that, too.
Must-know about this feature
Once you delete a User, the User cannot access the account. Deleting cannot be undone unless you add the User again.
Remove a User
Click on "USERS" from the bottom left on the sidebar
This will open the list of all existing Users.
Select the User you want to delete
You can do that by clicking on it.
Click on "Delete"
You'll find it on the right of "Save" icon.
Click "OK" to confirm
Once you do it, the User cannot access the planner anymore.