I would like to setup some interactive Power BI dashboards using an existing SQL Server database as a source (either with a Power BI Service in MS Azure or a Power BI Report Service on-premise).

As far as I know Power BI uses an SSAS Tabular instance internally. Would it be beneficial instead to use a standalone SSAS Tabular instance, load data into it and let Power BI access this separate instance with Direct Query? Could you name the advantages of this approach?