Sunny days can be useful for creating salable prints and stock photos. Images of people enjoying the outdoors are popular with a wide variety of clients from those looking for home decor, or pharmaceutical companies, clothing lines, the parks department, stock agencies etc.
In the afternoon, you’ll find infinitely more people than you would at sunrise or sunset. This is a good thing, as it opens the door to a whole new series of photographic possibility. By including a human element, the image will have greater reach as viewers can relate to it personally.