With Reason 13, it's necessary to switch between the Edit Area and Arrangement Area for certain tasks that could previously be accomplished entirely using the "top bar" above the piano roll in the Edit Area of Reason 12.
But unlike that top bar, the Arrangement Area in Reason 13 scrolls and zooms independently of the piano roll, which can make certain tasks feel more difficult or disorienting (think tasks that involve editing a lot of notes while also chopping, joining, and moving sections of a clip).
This feature would address that, because when the views are linked, the clip itself would serve the same roll as that top bar in Reason 12.
As a bonus, it would also let you use the Arrangement Area scrollbar to scroll the Edit Area (which no longer has its own dedicated scrollbar).