(Microsoft Word must die.)
The Plain Text Workflow is an alternative to writing with a word processor. Mind you, I said writing, not typesetting or formatting, which is a major part of what word processors do. The idea of the plain text workflow is that you separate the act of writing from that of producing a formatted, typeset final document. You initially capture your words using a plain text editor, perhaps using a lightweight formatting language like Markdown. Then, using freely-available software such as pandoc, you translate your plain text document into whatever file format you need to provide (to a colleague, reviewer, literary agent, journal editor, blog post, email, website, etc.), be it Microsoft Word, LibreOffice, PDF, HTML, or whatever. You might also bring this translated file into your word processor to continue tweaking the formatting. However, your original words are captured in one or more plain text files, which remain the source from which various other document formats flow. With the plain text workflow, you work in plain text, and all of those other document formats are outputs from your plain text source document.