Reproducibility is a severe issue. Writing code usually helps, because the code is like a journal of your work, especially if you combine it with literate programming techniques, which in R’s world is so easy to do (Rmarkdown, knitr). However, there’s one thing, which can cause some problems - the packages versions. Some of the old code might not work, because there were changes in the API or in the behavior of the packages (I’m looking at you - dplyr).