Why use a SSAS cube?

What are the advantages of using SSAS Cubes over a regular data warehouse for reporting? Note I'm not asking why report on a data warehouse instead of a OLTP database. which is covered at Why You Need a Data Warehouse. Think of it as if I have a reporting tool and have the option to link to tables in a data warehouse or an SSAS cube, what would be the benefits if I linked to the SSAS cube: