Is there a difference between the data loaded in Power BI and the data in OLAP cubes? NO is the answer.
When we have a data warehouse, why do we need an OLAP cube?
A cube's main purpose is to do precalculations and store the results in an analysis (in general, ssas) database. We generate an OLAP (or SSAS) cube instead of doing the calculations in the rdbms or data warehouse. As a result, the calculated formula's output is saved as a cube. As a result, the cube's core is a fact table, and the cube's dimensions are its faces.
There are various advantages to constructing an OLAP cube, but the most important ones are that we may prevent resource contention when doing analysis with the source system and that we can have data from multiple data sources for analytic processing (OLAP).
What's the use of an OLAP cube when we can import data from a data warehouse directly into PowerBI?
There is little delay because the OLAP cube stores the precalculated data for each query in PowerBI.
As a result, OLAP takes Relationships, Aggregations, Drill Downs, and Business Logic out of PowerBI and performs them at the cube level.