I had a special order for six dresses for a My Twinn doll. In the past, I have struggled keeping the collar and neck facing flat. I never bothered with staystitching; why would I waste time sewing another row of stitches. I looked at the pattern instructions and the words staystitching jumped out at me. I thought okay, let me look up staystitching on the Internet and see why I needed it. All the sites I visited praised the value of staystitching (it reinforces the neck and keeps it from stretching). Okay, I was convinced. I took the few extra minutes to add the stitching. It works!! Beautifully! Every collar I made came out great. A lot of times the collar would slide during sewing. I would have to rip out parts, stretch it, and sew it again.
So my advice to you reader, take the time and add the staystitching (especially at the neck). It will save you time in the long run by not having to rip out the collar or facing.