"Upload data" is something that's currently limited to the latest releases of BIP and the upcoming cloud version of OBIEE. However, the could version will not allow mash-ups since what you upload is what you model. There is no "central, IT-managed RPD" in the on-premise install sense. This will evolve obviously as the versions progress.
BIP uploads on the other hand provide - at the moment - to load your own data and the report on it. Downside: this covers XLS sources and you can't mash up data with OBIEE- / RPD-sourced information.And especially not access the metadata layer to hook up with an uploaded XLS.