I know this is an old post now but I finally remembered my resource and I like it when people follow up on message board posts.
This Berroco video
is where I got the idea for pinning pieces together and marking halfway points.
The title indicates that it's for set-in sleeves, however I use this for every typed of seamed sweater whether it's raglan or something else.
When I don't, I always end up having to re-sew at least one seam. Even when the stitch count is basically one-to-one, such as a side seam, I will somehow mess up the mattress stitch unless I do some pinning.
I hope this is helpful for anyone struggling with finishing confidence.