Is it a wrapper on top of datafusion, but with an ability to define transformations in yaml? I mean it looks really cool, I'm just trying to understand the usecase
Basically yes. The usecases I have found so far at work is to build an API around this to dynamically register automatic reports for data analysts, clients and non devs. In general this also greatly speeds up dev time for any ETL that we need to deploy (am part of a data engineering team).
Another usecase I found is that using the CLI tool we can create run books for our SRE team to run queries for debugging/data validation purposes. I think we'll find more as we go but another part of it was to simplify working with datafusion and deltalake as their APIs expose a lot of lower level stuff.