When personalizing your templates, you have available content set up in advance in the Recommendation engine. This includes text, images, and call to actions.
The Quick Edit functionality allows you to easily update visual content and calls to action by changing the label on them, or to add, remove or change the attached document or URL link.
These changes are not permanent and are only applicable for the email you are composing. If you are happy with the changes you made using the Quick Edit, you can save the template either in My Templates or Team's Templates. You can do that both before sending or after sending the email.