I wonder where the shingles are hiding & where the water might want to go…
Oh yeah & that results in this type of damage
Even with the shingles overhanging the sheathing by 2″, you still need to install a drip edge to prevent water from being wicked back by surface tension & wind. That is one reason why the drip edge has that little kick-out & window sills have a kerf on the bottom. For more on getting this & other flashing details correct; Getting the details right: 4 biggest roof flashing errors to avoid