Felt paper does one thing only, it gives you a second water barrier under your shingles. It will keep your house dry if you lose shingles during a storm or wait too long to reroof. Holding the bottom edge of the shingle even with the edge of the metal drip edge. The metal drip edge is a secondary drip edge only. Water will run behind gutters and cause mold, mildew and rot.
Water can get into the walls of brick structures and damage interior walls.
This picture shows two problems, the other being an incorrect installation of the gutter. Reroofing over old shingles will also reduce the life of shingles by many years. The added thickness which acts like insulation causes added thermal shock. Hot dipped galvanized nails not only don't rust but resist popping back out because their shank is very rough. The plated nail has a smooth shank.