What are the benefits of genetic variation?

In the case of a disease epidemic, not everyone dies.

Genetic variation allows for a greater chance of a population surviving. For example, if a plant species acquires a disease, without genetic variation the disease would just keep getting passed on to the next identical organism and the population would decline and eventually die. But genetic variation prevents that from happening, because you have so many other species in the ecosystem, and genetic variation is a product of sexual reproduction meaning that the offspring of the diseased plant has a possibility of not inheriting the disease.