Usage of R query in published report

In a report, I load files from a Sharepoint folder and then I transform the data using the R query editor. I also use an R visual in the same dashboard.

If I only use the R visual and don't perform the transformations using R query I can publish the report and schedule a reload. However, if I use R query the reload scheduling asks for a gateway. 

I don't use any external data, so, why is there a need for a gateway? 

Why there is no need for a gateway when rendering an R visual and not for running an R query?

Thanks in advance.