Of course it has other uses.
It's a pity that you still keep ignoring F&O documentation, because many of your questions are answered there. In this case, let me quote the page called Bring your own database (BYOD):
The BYOD feature is recommended for the following scenarios:
You must export data into your own data warehouse.
You use analytical tools other than Power BI, and those tools require T-SQL access to data.
You must perform batch integration with other systems.
In general, using BYOD make sense in many cases when you want to query the data by SQL. You can't do that directly against F&O, because you don't have access to the production database. This may be done for reporting, but also for an integration with other systems.
By the way, don't forget that you don't have just BYOD these days. You may use a data lake for similar purposes.
