Any user with basic Email Templates Permissions can add, edit and use their own Email Templates.
If a user has Branch or Corporate Permissions they can set a different Owner from themselves as well as Enable the Template to be used by others:
When this is done, a User who is under the Owner in the hierarchy will have access to the Email Template and can send it if they have Email Template Permissions.
The User sending the templates is able to select from any Email Templates that are owned by themselves or one of their parent entities that are Enabled for Other's Use.
If a User has Corporate or Branch Permissions they can also see, edit, or send any Email Templates that are owned by any User within their Permission Controls.