Making clean edges

Hi!
I’ve been watching some videos in making smooth edges. If I always slip the first and last stitch purl wise, am I correct in saying that if I am making a sweater… or whatever, if the directions read for example:
cast on 20 stitches… and then Row 1: knit the first three stitches… yada yada… so am I suppose to take the first stitch off purl wise and knit the next 2 stitches which would be the first 3 stitches?.. and would that apply to the end of a row, too?

Hoping that you understand my question.
Thanking you in advance.

Warmly,
cair:knitting:

You only need to slip the first stitch. However, if the sweater is in pieces and will be seamed I wouldn’t bother because the edges will be hidden. And yes, if it says knit 3 you’d slip the first and then knit two. At the end just do what it says with no slip.