Why particular question?

Rmarkdown is a composite of markdown and code. You can nicely separate free text, explanation, comments etc. from code. If you render the document you have code and figures in one document. That's great for documentation and version control. Many handy features, such as options to evaluate only certain chunks, caching etc. The only situation these days where I do not use Rmarkdown or its derivates is when I have a script with only functions to be imported into an analysis, or package code.