The reason to use R is because someone else has already made an amazing library(usually some kind of academic research) for it that doesn't quite exist for pyth

The reason to use R is because someone else has already made an amazing library(usually some kind of academic research) for it that doesn't quite exist for python yet. There is also an aspect that if you are using a technique you don't really understand you can do the same thing in python and R and compare if the results are the same.