When creating an Email/Letter Template, you may have noticed a selectable button that reads "Embeddable?". If you have clicked this you will see that that template becomes highlighted in yellow on the Email/Letter Templates page.
When you are composing a new template, you will notice a dropdown on the far right of the tool bar above your template body editor, which reads "Embed a Template". By clicking this and choosing the Snailer Template you saved as Embeddable, you will be able to quickly and easily insert a large bulk of text into your letter!
The purpose of this tool was for organizations who regularly update their letters that go out (via email or mail), but in doing so still want to retain a good bulk of the letter (e.g. an "about us" section in the letter). Instead of having to re-type in that bulk portion, you can simply choose to insert the tag into the letter, which will automatically insert the text from the initial template that was marked as embeddable.
Do note when you insert this tag into the body of the template, it will just appear as the "tag", not the entire body of what you typed out, which will need to be considered for spacing needs.