I use a curry comb every time I groom my mare. It's great for loosening caked on dirt and dried sweat, and my horse love it. Ursula lets the cross ties hold her head up and her lower lip sags halfway to the floor when I curry her. She just completely relaxes and leans into it, especially on her neck.
It is true that you should restrict curry and stiff brush usage to the fleshier areas, especially if you have a sensitive horse. I will occasionally use the curry on my horse's face or lower legs but only very carefully, and gently, and only if there is a specific reason to, such as a bit of mud on her cheek or something.
I use the curry by rubbing in circular motions, and working from the front of the horse to the back. I then follow the curry with three brushes, a stiff-bristled brush, a medium brush, and then a soft, finishing brush.