Living in Michigan, we all suffer from extreme weather that is capable of causing severe property damage. Believe it or not, city code only requires the installation of 2 feet of ice guard from the inner wall.
We have found that the only way to confidently protect our customers is to triple that amount of iceguard installed to a 6 foot minimum. This water proofing membrane gets installed around the perimeter, the entire length of every valley, low slope area, around the chimney, around all penetrations, and in any other areas that are prone to icing up in the winter.
The rest of the roof gets cover in a deck protecting underlayment that helps absorb moisture away from the wood while allowing it to still breath, thus preventing the wood from rotting out prematurely. You have the choice of either conventional #15 felt paper or synthetic underlayment for the same price.
Felt paper has been out for nearly 100 years now so long term we are very confident in its performance. Synthetic is the newest, latest, and "greatest" but has only been out for 5-6 years. It seems like a superior product that was designed specifically for its purpose but nonetheless we like to educate our customers up front so that they can make an informed decision.