Well, see my Copenhagen example abuve for one reason. The Metro goes every 5 minutes, but if you need to go somewhere where you need to switch between the metro

Well, see my Copenhagen example abuve for one reason. The Metro goes every 5 minutes, but if you need to go somewhere where you need to switch between the metro and some other form of public transport then you'll usually double the time required. The fact that it's cheaper for three people to take a taxi instead of going with public transport doesn't help either.