Moss, between and under tiles, expand when frozen, causing tiles to fracture which results in potential leaks.
With a heavy downpour of rain, moss growing on the roof can dislodge falling into your guttering, restricting the flow of water and blocking downpipes and drains. Rainwater from overflowing gutters can get into the eaves causing dampness and mould, and the soffits can also rot.
Your roof is the most important part of your home to maintain because it’s most exposed to the elements. If you want to keep your roof in good order, then keeping it clean is essential.