Wow! Not only unsightly, but here the roof deck is exposed and starting to rot.
Your roof is an integral part of the building envelope - don't let lack of maintenance, repair or replacement undermine the structural integrity of your home.
Here is an example of some nasty structural damage from a leak that was likely years in the making.
Regular inspections can often catch problem leaks before they result in such severe building damage and regular maintenance is crucial for the well being of your building...