It is important that the ridge is kept up to date because if it is left for a long period of time it can start to wear out the top layers of reed which in turn causes long term damage to the roof itself.
A worn out ridge can allow water to penetrate inside the roof rather than running down over the surface of the reed and drain off as it is intended to do. The ridge needs to be replaced about every eight to ten years, this is like the roofs mot as it provides the opportunity to re-ridge, clean off any moss and carry out any relevant repairs needed. This should then see the roof good until any further maintenance work is required.
A block or pattern styled ridge will tend to last longer than a flush ridge due to the thickness of the ridge.