Koen Verbeeck notes a new default:
The Power BI Enhanced Report Format (PBIR) will soon become the default, and that’s a good thing because it significantly makes git integration easier. You can already enable it in the preview features of Power BI Desktop (also enable PBIP and TMDL to make git integration of the model itself much easier).
Read on to see the administrative setting associated with this, as well as reasons why you should keep it on.