Library just gives you renderer with render function. It is up to you when and how you call it.
It's just that most of examples use requestAnimationFrame to call renderer.render, which gets called by browser when browser refreshes the screen (usually at 60 fps).
This makes sense when you can expect either changes in the scene or if a camera view changes all the time (most of examples are like this).
But if you know both your scene and camera will be static for a reasonable amount of time, you can update the rendering just at points of time when changes happen.
For example Editor refreshes the screen just when the camera or object changes:
http://mrdoob.github.com/three.js/editor/
Library just gives you renderer with render function. It is up to you when and how you call it.
It's just that most of examples use requestAnimationFrame to call renderer.render, which gets called by browser when browser refreshes the screen (usually at 60 fps).
This makes sense when you can expect either changes in the scene or if a camera view changes all the time (most of examples are like this).
But if you know both your scene and camera will be static for a reasonable amount of time, you can update the rendering just at points of time when changes happen.