In the case of the Sound Toll ships actually had to dock in Elsinore - I don't know if they could also dock in Helsingborg - to pay the toll; if they didn't dock cannons from both sides of the Sound would shoot at them. But you are right that Elsinore wasn't important because of the port; it was important because of the location.Apart from Constantinople/Istanbul it wasn't the ports that were valuable though, ships didn't need to dock to pay the toll.