When it rains moss soaks up all the water and them dumps it all in one place. If your roof isn't totally watertight you'll get leaks. Also in winter that water freezes and cracks your roof tiles. Which then leak in the spring.
TLDR Get rid of it.
I cleaned the moss off our kitchen extension roof a few weeks ago. Waited till it was real dry then had at it with a stiff brush. Roofer told me it comes off easiest either when it’s bone dry or soaking wet. Didn’t fancy climbing on a wet roof.
When it rains moss soaks up all the water and them dumps it all in one place. If your roof isn't totally watertight you'll get leaks. Also in winter that water freezes and cracks your roof tiles. Which then leak in the spring.
TLDR Get rid of it.