R is a free programming language and software environment for statistical computing and graphics supported by a not-for-profit organization.
Search engine optimization (SEO) is the process of improving the quality and quantity of website traffic to a website or a web page from search engines.
R is specialized in data mining, statistical and data analysis, and data visualization. It also has a good capacity for crawling. Basically, everything that is useful for doing some SEO.
When you have understood the fundamentals, R' is also quite easy to read and write. Even if you don't want to really learn it, just copy/paste 3 lines of code, you can crawl a website or extract some Google Analytics data and export CSV.
R becomes useful when you start to deal with big websites with thousands of pages. I'm a big fan of automation but the relevance needs to be properly evaluated. There are also a lot of great SEO tools out there, R' will never replace them but it is definitely a very nice addition to your set of tools.
Python is an extraordinary programing language, very versatile, in many cases faster. Python is better than R, 90% of the time. The 10% where R is superior is data visualization syntax (nothing beatsggplot2so far) and easy-to-use data manipulation (thanks to Dyplr ). Finally, it's less wordy, often easier to read.
Using R is a pragmatic choice, R is often used by academics and people that have another job, full-time dev logically learns Python.