My first impression of applied i-cord wasn’t really a positive one. I worked it on a sweater I made for my grandmother in 2006:

The i-cord around the neckline was tight, and in the Silky Wool it didn’t really provide a stable enough edge for the buttons. So I didn’t really give it another thought after that–none of the patterns I happened to want to knit used it, so I just forgot about it. When I was knitting Bryony this summer, I came across a bit of a stumbling block when I realized that I liked the way the tank front looked when it didn’t have an edging, but that the back neckline was just going to flop without one.
So how to work a neckline just on the back neck? I considered knitting an attached 1×1 rib border in a way I’d used in some lace projects, pulling my working yarn through as if I were picking up a stitch with it before working a pair of rows. (This technique made a later appearance in Twinflower, incidentally.) But I didn’t think the ribbing would taper properly, and I worried that it would be too bulky.
Enter applied i-cord. The ends taper naturally, you can work it on only the back of the neckline, and I figured out the trick to making it work without a pucker. Now, with so much more knitting experience under my belt, I realized that the difference between row and stitch gauge was the culprit in my grandma’s sweater: You need to pick up enough stitches to accommodate the row gauge you’re working the i-cord on. When I picked up around the neckline, at 1 per stitch, and then worked a tight i-cord, I was limiting myself to an insufficient number of rows and the fabric puckered.
So I picked up more on Bryony’s neck edge, and it looked beautiful.

I also decided to try my new-found insight and work the i-cord on the armholes, as well. I didn’t want a ribbed edge detracting from the clean lines of the cable and faced hem, and I was flush with my success on the neck edging. Again, they worked like a charm on the armholes. They tightened everything up nicely, without puckering, and provided stability on a garment section that gets a lot of tugging.
Here’s an armhole before the edging:

Loose, floppy, likely to expose a bunch of undergarment. And after:

I’m glad I gave it another chance!