Both the Simple Editor and the Advanced Editor generate a text version of every HTML email you create so you can simply copy and paste your text when you want to create a text-only email. Currently, you cannot directly convert HTML emails to text-only emails in the SimplyCast application.
The basic difference between designing HTML emails and designing text-only emails is that text-only means just what it says. The only thing you can include in the email is text. In an HTML email, you may have text, images and active links that a reader can click.
A text-only email works great if you are on a phone where you have a smaller screen or don't want to use a lot of your data on images, or if you are on a computer but the images are slow to load or you have blocked images from being received.
HTML emails may be more engaging and are often preferred as a reader can actually see the product being advertised and is able to click a link directing them to another page.
It just depends on how a reader is viewing the email.