Not sure what you mean? There are several place prone to lean on a roof. The vents and in the valleys. Valleys get 2 to 4 times as much water in them as the rest of the roof, so you always have to increase the amount of protection you put there. Here, they use Grace Weathershield on top of the paper. Before that came along, metal was the best way to deal with all the water that comes down the valley.
I'm not being critical, I do this for a living and it's both interesting to me how things are done in other areas, and I also like to offer suggestions when I see things that make me wonder if they are done the best way possible. I know up North that wood rot isn't as big of an issue as it is down here. You just paint the fascia and it lasts as long as the paint lasts, and in some cases it goes decades after the paint has peeled off and it's still sound. Here, you have to cover the fascia with something, and then you want the flashing and shingles to go over the top edge of the fascia to keep water from getting behind it. Even if you use gutters, there is water that gets behind them that leads to rot. And of course, the gable ends do not get gutters, so they are always exposed.
Eddie