When I first started knitting, I read the directions and they said to block before seaming up a sweater. I didn't know what blocking was and I really didn't want to waste the time, so I'd just sew it up and be done. Of course, my seams didn't lie flat, and I needed five hands to sew them up, but hey, I was done! Yee Haw!
Then one day (I can't remember why) I blocked my pieces, then I sewed them up. It was amazing! The seams didn't fight me when I was sewing them, they just lay perfectly flat and cooperative. The finished seams also were flat. I couldn't believe what a difference it made. Maybe the directions are there for a reason. Who knew?