What is the use of On-Premises Gateway for PowerBI Desktop application

Hi,

I am starting exploring POwerBI domain and trying to migrate my project SSRS Reports to powerBI Platform.

I have few Basics queries regarding this new tool. I would be thankful to you if you can provide me clarity!

I have understood the use and importance to Gateway for connection report to datasource in app.POWERBI.com site.

If i publish report from powerBI desktop to my Dashboard then in my dashboard(at app.powerBI.com) dataset.reportdata will not be refreshed untill i have gateway installed and configured.

BUT my Question is - Do i require Gateway for importing data in my PowerBI Desktop?

I experienced that i can get data from my server(on premise) to report in powerbi Desktop.

Thanks,

Sushant.