What moss actually causes
Heavy growth can break away and collect in gutters or valleys. Thick moss around laps can slow drainage and make inspection harder. On some tiles it holds moisture against the surface for longer.
A light covering is different. Removing it with harsh pressure washing can cause more harm than leaving it alone, especially on older or weathered materials.
Avoid pressure at laps
High-pressure water can drive beneath tiles and slates. It can also strip surface finishes from certain concrete tiles. If cleaning is justified, the method should suit the covering.
Access matters as much as cleaning. Roofs are not safe working platforms simply because the task sounds like maintenance.
Use the opportunity to inspect
If safe access is being arranged for moss removal, check slipped pieces, cracked mortar, valley debris and gutter outlets at the same time. There is little sense paying twice for access within a short period.
Photographs before and after are useful because cleaned roofs can reveal old patching that was previously hidden.
Recurring gutter blockages
If gutters fill with moss fragments every few months, deal with the source and make sure outlets are adequate. Gutter guards can help in some settings but they also need cleaning and can make inspection awkward.
The aim is reliable drainage, not a roof that looks newly scrubbed.