Does an R Script run once for each dataframe returned?

When using an R script as a data source, the menu gives you the option of which data.frames you want to load into the Power BI environment. If I select multiple data.frames, are those data.frames then associated with the same instance of that script? That is, if I update the data in the future, will the R script run only once to get all those tables again, or will it run once per each table returned?