Slipping a stitch at the beginning of your row can make it look really, really nice. However, it can also cause distortion and shrinkage at the edges. Slipped stitches are also easier to see and pick up, but it creates an imperfect ratio depending on your gauge. Likewise, slipped stitches can make it more difficult to seam, since seaming is done using the bar between the first and second stitch of each row. Slipping the first stitch of each row means you’ll only have half as many bars as you need. That will result in bigger stitches and a weaker seam.
The slipped stitch edge looks very different depending on the stitch(es) you’re using for the body of your work. On a stockinette swatch, the slipped stitch edge almost blends in completely. On the garter swatch, it’s a very sharp edge. On the seed stitch swatch, it’s a little softer.
When I first started knitting, I searched for techniques to keep my stockinette from curling, and I found a blog post that recommended slipping a stitch at the beginning of each row. I tried it, and I have to tell you, it did nothing. That’s because while it can tighten up the very edge of your knitting a tiny bit, slipping a stitch does nothing to affect the other stitches inside the piece of knitting.
Of course, there is room for personal aesthetic preferences here, too. I’ve seen a lot of articles and blog posts describe a regular garter stitch edge as ugly, lumpy, or weird looking. I don’t think that’s true at all! In fact, I actually prefer it to a slip stitch edge. To me, the slipped stitches look big and out of proportion to the rest of the work.
Depending on the look you’re going for, you might want to slip the stitch purlwise or knitwise. You should also consider whether you want to slip it with the yarn in front or with the yarn in back. All of these will create slightly different visual effects, and the best way to figure out which one you like is to test them out! Grab some extra yarn, knit up a swatch, and try different techniques along the edge.