Here's a secret. I use steam when finishing my knits. I pin the corners of button bands out, making them as square as possible, I give them a shot of steam and let them dry before I move the knitting. I use a tailors ham around the edges of my set in sleeves, I leave the first section to cool and dry, then I move on and do the next section.
Why do I do this? I have taken classes in both tailoring and millinery. It's very common for both disciplines to use steam in shaping materials. When making hats from wool and straw, they are steamed and stretched over wooden forms and then left to dry. In tailoring we use padded forms and wooden pressing tools to perfect seams and get into corners. We steam edges and use the wooden tools as weights to hold edges in place while they cool.