"The first principle of optimization is don't." 
Larger, more complex scripts, such as cascading menus and expandable outlines, can benefit more from download speed than from execution speed optimization. Realistic interactive games and simulations can benefit more from execution speed than from file size optimization. As you'll discover in Chapter 10, you can trade size for speed complexity and vice versa. Optimizing both size and speed while maintaining legible code takes a combination of techniques.