Pinked seams or edges are not recommended for garments that are to be washed. The practice usually, when ruffles are pinked is to have them and enjoy their frilly frothiness....
And what Mary Brooks Picken meant was enjoy them THIS ONE TIME, or brace yourself for a lot of work . Because she then counseled, take the ruffles off the dress, wash and iron the dress and the ruffles flat, and then “re-pink” the ruffles, or give up (not that she wrote that, but that is my interpretation) and sew lace or ribbon binding to the edges to finish the edges.
Pinked edges are raw edges cut into notches with pinking shears, or with a special sewing machine attachment, or a specially made pinking machine which is far easier. So you can see why a woman would say, ok, that was fun, but now I will trim with ribbon and not have to take off the ruffles every time I wear the dress.
On the one hand, Picken saw you could get tired of the process, on the other hand, she also wrote, “Once you own a pinker, you will find innumerable ways to use it” on garments and home furnishings. The sketches show pinked ruffles on a halter dress, along dress hemlines and necklines, as decorative roses, or flat pinking along the edges of collar and cuffs, even on the edges of a bolero jacket. Of course, pinking is most often used today simply as a seam finish for the firmly woven fabric. Clearly not as much fun as going wild with your pinker, which shows you yet another decorative embellishment that we have forgotten about.
This is from Modern Dressmaking Made Easy from 1940.