Hi John,
Here is the main reason for me. Since LR came out with first the pano merge, the boundary warp, I use it for almost all my panos. I tend to only shoot one row panos. The boundary warp, does an amazing job, much better than the CC photoshop content aware tool, or attempting to warp a cylindrical pano to fill out the blanks in CC photoshop.
I have a catalog full of 4, 5, 6 part stitches, all of which were worked up with local adjustments since they were done prior to the release of the LR pano tool, thus when I roll these into LR's pano tool all the adjustment work I had done so far (see previous post) is lost. Going forward not a big deal as I know to make the pano first, it's just the rework involved on all the older shots I would still like to revisit with LR pano tool, it's that good a tool.
Paul C