HEre's 10 Reasons to get your roof cleaned.

1. Improved curb appeal: A clean roof can enhance the overall appearance of your home and increase its value.
2. Prevent mold growth: Mold and mildew can thrive on a dirty roof, causing damage and creating a health hazard. Regular cleaning can prevent mold from growing and spreading.
3. Remove algae and lichen: Algae and lichen can discolor and deteriorate your roof, reducing its lifespan. Cleaning can remove these organisms and protect your roof.
4. Prevent water damage: Debris, moss, and other materials on your roof can block water from flowing properly, causing water damage. A clean roof ensures proper drainage.
5. Improve energy efficiency: A dirty roof can absorb more heat, making your home less energy efficient. Cleaning your roof can improve its reflectivity and lower your cooling costs.
6. Extend the life of your roof: A dirty roof can degrade more quickly than a clean one. Regular cleaning can prolong the lifespan of your roof.
7. Keep your gutters clean: A dirty roof can cause clogs in your gutters, leading to water damage. Cleaning your roof can prevent these clogs and keep your gutters functioning properly.
8. Improve air quality: A dirty roof can release mold spores and other pollutants into the air, affecting the air quality inside your home. A clean roof can improve indoor air quality.
9. Meet warranty requirements: Some roofing manufacturers require regular cleaning to maintain the warranty on their products.
10. Save money: Regular cleaning can prevent costly repairs and replacements in the long run, saving you money.

Here is an example of very dirt roof (Photo Below).  It has Heavy Lichen coverage on it.  This latches onto your shingles and over time will DESTROY them..

Check out this article from "Wet&Forget" about Lichen. Lichen Info