In version 1.15.0, we introduced the ExecuteStateless Processor. This was a quick win to allow running a flow using the Stateless Engine.
Since then, we have seen many users make use of it. However, it was always intended as a stopgap until we had the ability to truly integrate Stateless groups with NiFi. This feature will allow for much better integration between the two, allowing users to configure a Process Group to run as a stateless flow.
This will offer better performance by integrating directly with repositories and provide a much better user experience, not needing to save off the flow and configure a separate Processor to point to it, providing visibility into what's happening, better Provenance capabilities (as ExecuteStateless shows all events as having been performed by the one Processor), more seamless configuration, etc.