Do you look in the corners and see debris growing?
Valleys also collect debris and cause issues.
The valley runs to an inside corner and pushes debris down into the gutter which can in turn cause a dam.
When this debris is not cleared, it could cause issues such as blockages and overflows, either over the edge of the gutter causing damage to gardens or the sides of the house or water ingress into the roof and wall cavities. The gutters rust and the valleys and roof deteriorate under the loading of debris.
Even when the grass dies off and goes brown, it remains in the gutter slowly causing deterioration and blockage issues from the dead root system.
Pine needles should be cleaned regularly to keep them from building up in the gutter. This build-up blocks the gutter preventing water flow through the gutters. It also makes gutter cleaning an easier task each time as it is not compact and much simpler to remove. This photo is four months of debris on the roof valleys and in the gutter.
As you can see it is important to clean your gutters to keep them doing their job. Corners can cause build-up but straight gutter can get just as much in them too.
So when you see growth poking up over the edges, don’t leave it too long to get those gutters cleaned.