In sexual reproduction, gametes receive a random assortment of genetic information from their parents, which creates unique genetic combinations in the offspring.
These new genetic variations can result in new traits, some of which may be beneficial, harmful, or neutral. Natural selection can effect these traits, causing the amount of beneficial traits to increase in the population, with the opposite happening for harmful traits.
Mutations in sexual reproduction are important for creating and maintaining genetic variation in a population, otherwise evolution would not occur.