There are several layers within a proper roofing job that are necessary to provide the most protection against water damage. Of all of them, the first line of defense is to install drip edge flashing. Unfortunately, many contractors tend to neglect this step.
The elimination of this installation can end up being your future nightmare. So, if you are re-roofing your house, be sure to demand a drip edge. If your roof is already finished (sans drip edge), you can still do a drip edge retrofit installation.