We just had the interesting experience of doing a private OW class for a friend's daughter. She started the class in a rented jacket BC; she didn't like it at all, and did some of the class in her mother's back-inflate BC. At the end of the class, she used one of our backplate setups (Hog harness) and was completely smitten. She said, "This is SO much more comfortable -- I know my mom is going to be mad, but I'm going to tell her that this is what I want."
Diver0001, one of the SB members I most respect, makes the point quite frequently that a good diver can dive well in any kind of gear, and he is totally right. But a beginning diver needs the most help -- and the one thing a backplate does is to keep the tank solidly put on the diver's back. In addition, in cool or cold water, moving five or six pounds up onto the diver's back helps make a horizontal position in the water easier, and there are a lot of reasons why a horizontal position is desirable.
Padding, extra d-rings, pockets, and integrated weights look like very nice features when you are starting out. But look around you at the divers who are really actively diving years into the sport. As my friend Mo2vation in Southern California has observed, "The longer and harder you dive, the more your buddies will look like us." Some things just work; other things seem attractive, but over time, one learns their drawbacks.