Sun, as we know, is essential to life on earth, emits the necessary energy for life to be possible on earth, without it earth will be so cold that all liquid water will freeze. Even more hydrological cycle would be affected as the sun's heat allows water evaporation and the continuity of the water cycle.
The quantity of sunlight we receive on earth depends on the total solar radiation that reaches earth, the solar angle, earth's orbit variations and how much radiation is absorbed, and how much is reflected. Approximately 70% of the radiation is absorbed and 30% reflected, this warms the earth generating an increase in temperature, without it, the mean temperature would be -18°C instead of the 14°C we have.