As a traveler, you’ll probably be taking public transport and online chauffeur services while in Tokyo. Even though taxi drivers will adhere to traffic laws, if you want to get a good view of your surroundings, you can push the slow-down button. This will let the driver know that they need to slow down.
There isn’t a lot of drag racing or drifting in Tokyo, unlike what you might have seen in movies. However, taxis can go pretty fast, and the turtle taxi button will inform the driver that you’re not comfortable with their driving speed. If you know a bit of Japanese, it would be politer to tell the driver verbally.