Tree leaves, moss and other residues can get deposited in the gutter, prevent the efficient flow of rainwater and clog your downpipes.
Regularly maintaining your gutters & downpipes gives them a longer life and reduces the risk of rainwater blockage. If you leave your gutters & downpipes blocked then it could end up causing some severe damage in the long run. If the water is not removed, it could break the gutter and even weaken the house, the façade and the foundations.