The main purpose of the gutters on your roof is to channel the water away from your house and its foundations.  Gutters help reduce erosion, leaks in the basement and other damage that falling water can create.

Gutters are manufactured from materials like cast iron, aluminum, steel, copper, zinc and plastic.  It is important to have the proper filtering system on your gutters to ensure that debris, like leaves and twigs, are not trapped and do not cause problems.  This filtration system usually simply consists of a louver or a screen, which traps the unwanted debris.

Most modern gutters require little maintenance.  You must make sure however that they are periodically cleaned out and the debris is removed.  Not only can water leak down the side of you home and cause damage, but also in the winter months, clogged gutters are cause of ice dams.  Ice dams result in the snow melting, and the water trapped on the roof.  Ice dams can cause serious damage and be a costly repair.

Source:  http://www.kitchentips.org/kitchen-appliances/basic-guide-to-rainwater-gutters/