This might seem simple and a little detail but large projects using linked files have needed this ability for a long time! Something so important but so subtle and little in just another dialog box among many.
This little check box means that your linked exterior curtain wall project can provide the room bounding your core/shell/interior project needs so you can avoid creating lots and lots of room separation lines. I'm also interested to see if users can harness the feature to enhance Unit Plan workflow perhaps. Happy Linking!