1) Type of reproduction that involves fusion of gametes that are produced by two parents is called sexual reproduction. Organisms produced by sexual reproduction are not identical to the parents. Thus it gives rise to genetic diversity.
2) The variety seen in plants around us wouldn't have been possible if the plants had not reproduced sexually. Plants and plant products have several uses for humans. For instance, they are a source of nutrition for humans as well as they are used for medicinal purposes. Thus we are lucky that plants reproduce sexually as we have access to multiple products.