Open some normal tabs and some incognito tabs.  On tablet, close all of your incognito tabs by tapping on the tab close buttons.  (On phone, there is no way to directly close tabs, but this can be done programmatically and some tests do so.)

After closing the last incognito tab on tablet, with the UIRefresh tab enabled you are immediately shown your normal BVC.  With the flag off, the old behavior was to drop you into the tab switcher.

On phone, the old behavior was to show your normal BVC immediately.

Once we move to a single tab grid implementation, I think we should have the same behavior across device types.  I think dropping into the tab grid feels like the better option, but this can be up for discussion.