In the context of an Enterprise wide solution Power BI tends to be used more at the beginning and at the end of an Enterprise wide Business Intelligence solution. The rest of the time the Enterprise wide solution architecture needs to be developed.
Power BI tends to be used at the beginning of an Enterprise Business Intelligence project since Power BI is an excellent prototyping tool.
Power BI tends to be used more towards the end of an Business Intelligence project once the data warehouse / cube has passed the initial testing and the self service report delivers have been fully trained.
I hope you find the diagram in the following link helpful ..
As always your constructive comments are most welcome.