I should take a picture of my last stitch wonkiness. It's what you do with it on the next row that takes care of it.
I don't slip for seaming for two reasons: One, I don't want to think of it--I just turn and start knitting--old habit I guess; and two, I like having the same number of stitches as rows. I don't think it makes all that much difference, but I guess it's just what I'm used to. So it's not really a matter of whether or not it's recommended, for me it's just personal preference/habit.
For the nice edge, even in garter, you can slip the first stitch. Garter prevents the rolling, slipping keeps the edge smoother.
I did one pattern where the directions called for a specific way to slip the stitch, and after I did it their way, I realized that it made picking up stitches in the next section much easier. So if a pattern says to, and it's not just for a seamed edge, I follow the directions.