why and when, a vector3's position need to be normalized?

[piglite]

When I read the example canvas_lines.html, all the geometry's vertices positions were normalized, is it necessary? yes, it's look like a little different with use normalize or not, but is it just for a good-looking?

[WestLangley]

In the canvas_lines example, the normalization was just for appearance. Examples where normalization is required are when a rotation axis is specified, or when a ray direction vector is specified.

[mrdoob]

Yes, it was for controlling the look. If you move the camera backwards you'll see it has a sphere shaped form. If you don't normalize the random numbers you usually get a cube shaped form.