Roofs are supposed to be on top of everything else. When a roof meets a wall you've got water running down where it was not meant to and then when it gets to the base of the wall it can wrap around and cause trouble. I just inspected a house that needed a whole new joist and its support replaced due to the lack of a few dollars of kick-out flashing.
This gutter valley splash guard will help prevent overflow from high pitched roof valleys. Click on image for link.
