I don't recall any mention of this appearing in the What's New documentation or presentations. I stumbled into it the other day and meant to write about it but my aging Dell finally bit the dust and that distracted me. I find this new parameter and options appears when I examine the Walls tab in the Copy/Monitor Options dialog.
Interesting isn't it? I experimented with using the option. This image depicts a linked file with compound architectural walls being used to create Stud Only walls in a structural model.
I specified that C/M should create a Stud Only wall type instead of the compound wall type being used by the architectural model. I then used the Location Line: Core Face:Exterior.
I didn't find any help documentation to support this new feature. What I did find declares that C/M just uses the Wall Centerline for alignment, which was true until now!
Also, fwiw the openings created at the doors and windows are the correct sizes but only because the families don't have any additional geometry beyond the extent of their frames. I placed openings in the walls at the curtain walls manually using the Wall Opening tool (Architecture or Structure tab > Opening panel > Wall).