Documentation is essential to any project and it can really "make it or break it".  However documentation is time consuming to draft and can sometimes be forgotten, or updates and amendments to it left behind as the project moves forward.  Additionally, creating your documentation with Markdown has its limitations, so you may not end up with the result you want or that your contributor needs. 
By using MDX you can combine Markdown with code and integrate it into your React project.  Documentation becomes a more streamlined and efficient process and dare I say it...fun.