The new boundary warp tool is evidence that Lightroom CC updates contain a lot more than new camera and lens profiles. From time to time Adobe sneaks in some life savings goodies. The recent dehaze tool is great for fuzzy photos and can be used in multiple ways. For me personally however, panorama and HDR stitching are the most handy tools because they reduce visits to Photoshop to a bare minimum. Generally, panorama stitching in Lightroom provides better out-of-the-box results than Photoshop, with less warp and less need for geometric corrections.
The new mighty boundary warp tool for panorama stitching in Lightroom CC 2015.4 is dead easy to use. When you are in the panorama preview, just below the projection options you have a new slider that has a 0-100 range. Lightroom fills in the peripheral gaps of the panorama with stretched and warped sections of the stitched pixels. Slide it all the way to 100 on the right and there is no need to tick the auto crop option!
I tried it with a three week old stitch. Here it is without the use of boundary warp, unprocessed, including my shadow (left in on purpose).
Now check exactly the same job with the boundary warp slider at 100. The cloud portion looks great. The same for the bottom part as well. Notice that my shadow has now been transferred to the very bottom right corner while there are no noticeable deformations:
The above example demonstrates very well the added flexibility we now have for cropping. Even if warp takes place in uninteresting portions of the panorama periphery, there is a lot more one can do with straight cutouts. The other option you have is to of course dive in the warp section of the free transform tool in Photoshop, something that adds an extra layer of time consuming manipulation.
One other area where boundary warp will definitely come useful is architectural photography where the extra area will result in better spaced out results after corrections for verticals have taken place. Now is obviously a good time to revisit old panoramas and check out if they can be further improved.