When you have a good idea, get more mileage out of it by creating variations on the same theme. That is the foundation for ad campaigns, houses in a subdivision, a series of paintings, and a symphony. The theme itself must be strong for the variations to be successful. Some elements remain constant throughout the group, but each variant stands on its own even without the others.
Variations on a theme are desirable for establishing a common identity among the discrete parts. When you bring about a positive response to one instance, it usually transfers to the rest. That is why the concept is so important to corporate image.
When generating ideas in the creative process, variations can be part of that phase. Perhaps one variation will stand out as being better than the rest. In the execution stage, you might want to create some variations to be able to offer choices to your client.