2 instances of image in Library?

Forgive me if i sound stupid!!

When i want to import an image from an external source, i use File > Import > To Library.

Now this image is in the library stored as a bitmap.

In order for me to work with this image, i have to Convert to Symbol. When i convert to symbol e.g graphic or movieclip, Flash MX adds another instance of the image in the library? So now for this image there is 2 instances in the library, a bitmap and a graphic or movieclip (whichever i choose).

Why does there have to be 2 instances of one image in the library???
Surely this takes up more space?

Am i doing things the right way???

Hope someone can help.

Thanks in advance.