Object Styles: Size and Position relative to spine
When setting an object's position with this feature, one must choose left or right for X position. With Anchored Objects, we can choose for that to be "relative to spine" instead. So instead of "left" or "right", we can choose "inside" or "outside".
This would allow for symmetry on a spread. Example: an object could then extend from the spine, beyond the page edge, through the bleed, whether on a left or right page.
Scott Falkner commented
Agreed. Much wanted feature. So much so it’s a mystery why it wasn’t included.
I fully agree with @Steve Laskevitch. I place Charts by Script and for that right now two Object Styles are given (left handed and right handed page). With the spine feature one Object Style would be enough.