From the manufacturer of Z-stop
Why remove moss or fungus at all?
Moss can severely damage, even destroy, a roof, by breaking down the fibers in the shingles, forcing them apart and allowing leaks to occur. Many roofs must be replaced prematurely due to damage caused by moss that has been neglected. Fungus, algae and mildew are less damaging to a roof than moss, in terms of actual destruction. However, it looks terrible: the roof on most houses is one of the largest visible surfaces, and when it is covered with fungus, algae or mildew, it detracts from the appearance of the whole house. Another reason is that fungus reduces the ability of the roof to reflect away light and heat, thus making for higher air conditioning bills.