At the time of the Class Field layout overhaul, new options were created with CSR JDK-8237976, including UseEmptySlotsInSupers in case users had dependencies on the old implementation of field layout.

I did a google search to see if this option was recommended in the OpenJDK.  There were some hits for applications that needed to be updated, like https://github.com/reactor/reactor-core/pull/3168. Who subsequently updated and fixed their applications.

The Vahalla project for JEP 401 is making substantial changes to the field layout code for flattening value fields, and the extra code to support this unused option is unnecessary work and could affect whether the VM decides to flatten a value field.