Using symbols in Flash provides two main benefits: reduced file size and ease of editing.
When you create a symbol and place instances of that symbol on the Stage, your movie’s file size is reduced because no matter how many times you use it, the code required to define it is only included in the file once. Each instance just points to the symbol and describes any modifications to that symbol, such as transparency or size.
Modifying work later is also much easier. Imagine that you’ve placed 100 blue squares (not instances of a blue square symbol) throughout your movie, and then you decide to change the color. You have to find and change all 100 squares. But if you made a symbol of a blue square and placed 100 instances, you only have to change the symbol, and the 100 instances are updated automatically.
Symbol-Editing Mode p. 30
When you have an object on the Stage that is a container for other objects (groups, symbols, and text boxes), you can just double-click it to “get inside” and edit the contents.
To exit the editing mode of the container, you can double-click outside the bounds of the container or use the Edit bar.
Transform Objects p. 31
When you’re scaling vector objects (those drawn in Flash or imported from Illustrator or Fireworks, as in the logo file.) you can increase or decrease the size without any negative effects. However, if you’re working with a bitmap image, you’ll want to avoid enlarging it. An enlarged bitmap has to be resampled and can become distorted or fuzzy. It’s best to open the image in an image editor such as Adobe Photoshop and scale it to the size you need.