The synodic period is equal to infinity when the periods of revolutions around the Sun of a certain planet and the Earth are equal for an observer from Earth. As you know, there is no such real planet. But in the solar system such a situation takes place: these are dusty satellites of the Earth for an observer from the Moon; asteroids “Greeks” and “Trojans” in orbit of Jupiter, and Jupiter itself in relation to each other; some satellites of the giant planets.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.