Did you know a Hexagon can be constructed using the angle pi/3 a lot of times? This is because a hexagon is made of 6 triangles with equal side length - the radius of the hexagon. The inner angles of these triangles is pi/3. Using this information and the trigonometric functions sin and cos can be used to draw such a picture.
You're right. But as the other commenter suggested, if you're on an embedded system or otherwise limited system, or even using another language missing certain constants and/or functions, it's a good thing to know.
You could also just pull the constant from memory, assuming you have the brain memory space that I apparently have...
3.1415926535897932384646233832795020841971693993751