First, this is about scalability of your application and not your data analysis. If your application itself has a lot of writes, it may require to shard your SQ

First, this is about scalability of your application and not your data analysis. If your application itself has a lot of writes, it may require to shard your SQL database. That may be easier using NoSQL. Also, NoSQL has advantages other than scalability. RethinkDB has a more pleasant query language (arguably), shamelessness (meaning it is easy to add a column), build-in ui, ...