Slip question

After casting on my stitches in cable cast on, the directions say to slip one stitch as if to purl, on every row, and after I slip the stitch as if to purl, I p1,k1,p1,k2,p2.
My question is, why slip the first stitch of every row? It isn’t increasing or decreasing anything, so, is this simply to make a pattern?

The purpose to slipping the first stitch of every row purlwise is to make a chained edge. It’s not necessary, mine looks worse when I slip it, than when I knit or purl the first one. You can do it both ways and see which you prefer. If you don’t want to do it, you would knit the first stitch in the pattern above.