Hi, 1) A low pitch roof allows water travel sideways through the Headlaps.
2) A steep pitch roof allows water to bullnose/twist up under the edges.
After about ten to fifteen years, your edges WILL have stainning, dry-rot, and decaying rot, along the edges at the top of the trim, the framming studs, and sheethings. Inward to about a foot !!
An all weather, all wind, all bug, all fog and most importantly,...all costs, method I use:
First make sure the trim, framming studs, and sheethings are in good condition after stripping off the old roofing.
1) Apply Ice and Water barrier ( a roofing product ) vertically down the edges all the way down to the eaves, making sure to overhang the product a half to three quarter inch past the edge. ( for bowed or rough edges, overhang more and cut to fit with a razor knife. )
2) Run your hand or a tool down alog the edge to create a fold line. ( this will allow the product to corner the edges )
3) Apply the dripedge from the eaves up, lapping only a few inches. ( it is very important to make sure the nailing is in a zig-zag pattern, every four inches, catching the top of the trim and sheething, or the metal will warp in between fasteners. )
4) Apply a six inch strip of Ice and Water barrier over the dripedge and the sheething seam, and roll it down to ensure contact. ( use smooth faced product on the Rakes, it bonds together best. ) Always use 8 inch dripedge.
These four stps will keep out the water, wind, bugs, fog and light. (but not me)
BTW....The felt paper is fine getting wet while still rolled up,...it is when it is applied that you best not get it wet before roofing over it. ( it will wave goodbye to ya )