So I do use the lens at extreme shifts routinely. There is also little fall off on this lens at the corners so there are no stiching problems in that regard either. I do this with a 45 TS too. They both make stitching the images in PS very very easy and I don't have to fool with the nodal point. These are good lenses.
My TS-E 24 suffers from significant vignetting and poor resolution at the edges and corners. This is not a problem for stitching, however, because the overlap areas are always around the central area of the image circle.
Stitching the 2 or 3 images you get using shift on these lenses is a breeze. The following image was stitched automatically with Panavue's Image Assembler. Nothing could be easier and quicker. I show it here with no modification or crop. This is how it looks, straight from the stitching program.
But look at the strong vignetting at the edges. However, vignetting can be fixed in PS (filters/distort/lens correction). It's the resolution fall-off I don't like. Let's look at the bottom left corner, lightened so we can see more clearly.
This is a 100% crop with jpeg compression at maximum quality. It's just not sharp and the noise is so bad in the shadows one would think I'd used ISO 800 instead of ISO 100.
Let's look at the top right corner. The fact that this is also not sharp doesn't matter in this image because I'll probably lose that corner when I apply some perspective correction in PS. Nevertheless, that corner is very unsharp.
Just for comparison, let's have a look at the centre of the image. This is reasonably sharp. At least as good as my Sigma 15-30 at 24mm, perhaps marginally sharper. I haven't applied any fancy sharpening routines to this image. Just the default sharpening in ACR. This is another 100% crop.
For this image I used a 5D with attached L bracket which slides on a clamp fixed to the tripod. This set-up enables one to effectively shift the sensor around the image circle, but in a rather clumsy manner. Since Image Assembler stitches such images perfectly, whether the lens is shifted in relation to the sensor, or the sensor shifted in relation to the lens, I sometimes don't bother loosening the clamp to slide the camera body along. It takes more time and in a situation like the above, one doesn't want a tourist wandering into the scene .