When building an Xbox One Streaming Install package (makepkg.exe) The layout generation code in Unity will assign each scene and associated assets to individual chunks. Unity will mark scene 0 as being part of the launch range, IE the set of chunks required to launch the game, you may include additional scenes in this launch range if you desire, this specifies a range of scenes (starting at 0) to be included in the launch set.
(NOTE: This option is meaningless for those using their own layout file, using a custom layout file is considered the correct way of handling more advanced packaging requirements).