Why write an R package?
R packages and the Comprehensive R Archive Network (CRAN) are incredibly important features of R. R packages provide a simple way to distribute R code and documentation. Packages on CRAN are basically guaranteed to be installable, as they are regularly built, installed, and tested on multiple systems.
And R packages really are quite simple to create. It used to be that the documentation format was a big pain and so a big barrier to writing a package. But Roxygen2 has greatly simplified that part, and so it should no longer be a barrier.
Write an R package to keep track of the miscellaneous R functions that you write and reuse. If they’re in a package, it’ll be easier to keep track of them, and so you’ll be much more likely to reuse them.
Write an R package to distribute the data and software that accompany a paper. This really is the easiest way to distribute R code and associated data.
R packages can be big and important, but that shouldn’t scare you off. I can’t emphasize enough: assembling a few R functions within a package will make it way easier for you to use them regularly. You don’t need to distribute the package to anyone.
Now go to the page about the minimal R package.