Large seams on garments is not something modern manufacturers do.
Remember in the Victorian times when large seams were left in everything. Recently I had a garment brought in that had become too small. I had a look inside and there were massive seams all the way through the garment. HOWEVER........... Someone had decided that it didn't sit correctly on the curved sections or at joins, so they had CUT through the seam allowance up to the existing seam!!!!!!!!!!!!!
For the life of me I do not understand why someone would do that. If you want to leave a reasonable seam allowance, then do that. You can even fold it over if you like and stitch it down with a loose stitch. If you have to clip, then consider folding the seam allowance over and stitching down rather than clipping. If I am reshaping a neckline or putting on a collar, you have to clip to get the curve, so clipping is important, but if you have want to leave large side seams, you really do not need to clip (usually).
In the case of the dress in question, it was not a fitted dress, so it could have been left without being clipped.
Happy altering
Judith aka genie