The slip stitch brings the height of the last stitch down before making the needle join. The end of the piece is smoother and the finish off is not so apparent.
In the same manner, if I'm working with a taller stitch, like the half double crochet, the last three stitches I make are two single crochets and one slip stitch to bring the height of the stitches down, and only then I make the needle join.
Give it a go and let me know what you think!
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