typically, I do knit the first and last stitch on my purl rows (they already are on the knit rows.) This creates a one-stitch wide garter column up both sides of the garment. It helps me seam, yes. But moreover it prevents the large loopy purl one typically gets on one side. It also gives a "finished" effect on the edges - so, seemed or not, it looks better. You can accomplish the same thing by slipping the first and last stitch on the purl side - if that's easier for you.