It's recommended that you always iron each seam (at least that's what they said in my highschool sewing class). When you sew up seams of pants, it's better that you iron them flat to expose the seam and flatten out the fabric. This is virtually impossible to do with both sides of each pants leg because of the scale. You can iron the seams flat after sewing the legs together but then you will end up with pleats, and sometimes pleats don't belong on an outfit. I made up my own "ironing ham" by stuffing my toddler's sock inside the pants leg and ironing the seams open. It worked wonderfully.