Slipping stitches

so i’ve seen some different instructions/helpful hints around, about slipping stiches… and those instructions say to always do it purl-wise unless knit-wise is specifically instructed… anybody know what the rationale for that is?

Slipping knitwise twists the stitch on the right needle so whether you slip knit or purlwise depends on the look you want or the pattern designer is trying to acheve.