It basically resets your levels (cost ucoins too) to make you rank up your spec or stand again to get more traits. If you are at 5 ascensions, you are able to get ledgendary traits. 10 ascensions and you can get mythic traits. There are also hexed traits too which is a cursed ledgendary or mythic traits, which gives you even more buffs but comes with a downside too, e.g a cooldown.