To slip or not to slip: that is the question

(DD is sick today and I'm at home with her. She's napping, so I'm blogging.)
So I posted this question on the knitty board and knittinghelp board and thought I'd post some updates and pics here: I've heard that for joining pieces, slipping the first st of the row makes joining easier. Is this true? What's the result of slipping? of knitting? Do you slip p-wise and k-wise, or only k-wise?

Following with the rogue in me, I decided to slip both k and p-wise for the cardigan. I don't know if I'm doing it right, and after looking at the edges, I'm not convinced it will be easier to piece. The edges roll in like mad - I think I'll have to block it before piecing together (are you supposed to block before piecing?? Again, I'm revealed for the poser-knitter that I am).

After my first intermediate knitting class, I was worried I might not get much out of it. All of the other knitters seemed very new, and the instructor didn't work with me at all. However, last night she gave the following advice about slipping: don't do it unless you're knitting an unseamed edge (like a rollneck edge). She showed me seams on a raglan sweater she knit. I swooned. Literally.

Anyhoo, so I'm going to follow her advice for now (not to slip my to-be seamed pieces). I'm also going to block (per her advice), and most importantly, I'm going to take the pieces to her to teach me how to seam them.