We are trying to build a data warehouse prototype and we are architecting in the below way
Source - > Staging DW (via ETL) -> Prod DW (via ETL) -> OLAP Cube (SSAS) -> BI Tool
In the past when I have worked on other warehouses, the BI tool usually sits both on the DW and the cube but in this case we are trying to see if we can do all the querying and reporting building via the cube (especially because the cube technology has come a long way and rebuilding a cube is not costly as it used to be and disk is cheeper than what it used to be). The one clear advantage I see is that the BI tool will have much better query times as it's going to be on the cube. However, I am not sure if we are missing anything by giving away by not exposing the database layer on the BI tool.