Is genetic diversity beneficial

When all the organisms are exact genetic copies, you don't have diversity. Additionally they would all appear as identical twins. If you are talking about a food crop if a bacterial, fungal disease strikes, they may all succumb. We would be left without that food. When there is diversity, some of the organisms are resistant. The resistant organisms survive and pass the resistance on to future generations. The resistant organisms also serve as a buffer. The resistant organism doesn't come down with and, therefore, spread the condition.