If both the opening song and the ending song are written, it can represent a TV series. For example, when the theme song of "Shanghai Beach" rings, everyone will think of that TV series, which is a symbol. Moreover, the opening song and the ending song can give people a basic understanding of the cast, and sometimes they can leave suspense in the film to attract the audience to continue watching. There is also a TV series that was completed by many staff members, Qi Xin. There are also many sponsors. The opening song and the ending song can reward these behind-the-scenes heroes and make their names known. The ending song is also a good time for big advertisements and can win money.