Like peanut butter and jelly, soffit and fascia just go together. In fact, they really do work together, but fascia is like the star, while soffit does the work behind the scenes.
Fascia is mounted on the exposed ends of rafters or the top of exterior walls to create a layer between the edge of the roof and the outside. In addition to serving an aesthetic function by creating a smooth, even appearance on the edge of the roof, fascia board also protects the roof and the interior of the house from weather damage. Not all styles of home will have fascia board, but many do.