Volcanoes have done wonderful things for the Earth. Volcanoes helps the planet mentain moderate, life living temperature Volcanism makes the planet habitable and without it, life on Earth would be non-existent. It also had directly and indirectly benefited mankind. The water that we see on earth mostly came from volcanoes. Other than the sun, volcanoes and geothermal heat also keeps the planet warm. The Earth's core produces heat, and the volcanoes releases them.
The ash and elemets released by the volcano can act as a natural fertilizer, thus creating fertile soils and producting increased harvest in years of the following eruption.