The simple fact is, keeping your roof clean can help it last longer while looking nice and clean in the process.
Lets say you wait too long, and its time to sell your house. Now that you have a roof that is 15 years old with moss growth on it, the buyers want you to have it removed as part of the sale agreement. We see this often. We then go out to your home and give you our inspection report which states that the shingles should not have moss removed due to lack of maintenance, wear, and the age of the shingles. That moss removal would further enhance the deterioration of the shingles. It would have been much better to have the roof treated every year, which would deter moss growth and keep it clean while minimizing foot traffic and scraping or washing.