I've been fitted, and have the measurements from that session. They turned out to be extremely close to what I had already determined I needed, by shooting at a plate and making dimensional adjustments myself. That said, the only thing knowing my measurements are useful for is when looking at guns online, or ordering a gun. I can usually know, within a range, if a gun is unsuitable for me by examining the dims on it. But, nothing can take the place of shouldering the gun a few times. I can mount a gun and know immediately if I will be able to shoot it reasonably well. Years of shooting different guns is worth a lot.
"not all my sxs are the same measurements, but pretty close at the face, which is usually about 3" back from the comb but could be different for you."
My preference is to only have sxs that shoot to the same POI (or very close to it) so that I don't need to make any adjustments when I go from one shotgun to another one. I'll shoot a new purchase at targets and at a pattern sheet at 16 yards. If I feel it's needed, I will have the stock bent.