Ascension is merely part of the storyline. It has no effect on your actual character. Although, after ascencion you find yourself in a part of the game where mostly everybody is level 20 and "ascended". You ascend in the desert and it is near the end of game.
Do a search before posting a question next time. And with a recent update, you now have to be ascended to enter Fissure of Woe and Underworld. If you want more info on ascension and/or Fissure of Woe and Underworld, search the forums.
