Ok, so calling this a full-on legit sewing method would be a bit of a stretch- it's just a really useful shortcut I've found for sewing stripes together (for matching when cutting, here's a helpful tip). This post may very well have TMI, but I guess the more you know...?
I first bought Steam-a-Seam lite 2 because it was recommended to finish knit hems before I bought a coverstitch machine. That worked very well, and I've found many more uses for the stuff. It's great for placing pockets, appliques, sleeve cuffs- anything you want to stay perfectly put while sewing. There are some jobs pins are just not great at. I prefer Steam-a-Seam to using a fabric glue stick now, because it is easier to apply without shifting threads around.
This technique is especially helpful with matching stripes, plaids or prints on stretchy knits or when working along a bias cut or curved seamline.
IMPORTANT: Make sure you are matching the stripes on the seamline, not the in the seam allowance. You will need to flip up the entire top pattern piece to see it is matched as perfectly as possible along the seamline.
Press the seam in place with your hand first- straight up and down.
This is the best part! Stitch using whichever machine you are sewing with. No stopping to take out pins or check on those stripes!
Note: I've never tried using Stitch Witchery or any other kind of fusible web for this purpose (and they may work), but I know that the Steam-a-Seam has yet to gum up any of my machines or needles. No $$ endorsement here, just truth.