Well, McKenna is now three years old, so I thought I would post about the 4 S's from the perspective of her being an older child.
I really liked our 3 S's we used and I plan to do them with my next child.
I continued to hold McKenna with her face over my shoulder while I sang her sleep-time lullaby until she was around 2.5 or so. I was amazed that every time we went into her room, I held her like that, I could literally feel her body relax just like I did as a newborn. She was instantly ready for sleeping. I found this to be fabulous because toddlers are often very wound up for nap time, so it was great to have something like that to calm her and prepare her so quickly.
Once I became pregnant, I knew that this wasn't something I was going to do as a large pregnant lady, so I started putting her in her bed while I sang instead of holding her. She has done just fine! She sleeps great and hasn't protested at all with the change.
And so my conclusion is that this action of the 4 S's did not create a sleep prop. It was beneficial not only for a newborn, but for a toddler as well. It didn't cost me any more time than I would take to put her to bed anyway. Therefore, I find it very valuable in helping your newborn baby to sleep. It is definitely not a move I regret making, and it is a move I intend to repeat.
See Sleep Training: The Four S's for more.