For someone who commutes daily and has a choice of lines, deciding which commuter pass to buy (and which one to claim from your employer) can be a pretty big deal. But for a tourist in Japan for a couple of weeks, trying to travel with Tokyo Metro rather than with Toei might save you the price of a can of soda. You'll probably need that can of soda to quench your thirst from the extra walking you do by not taking the easiest route.