<HTML4.01: Visual presentation of images, objects, and applets>
The height and width attributes give user agents an idea of the size of an image or object so that they may reserve space for it and continue rendering the document while waiting for the image data.
</HTML4.01: Visual presentation of images, objects, and applets>

http://www.w3.org/TR/html401/struct/objects.html#visual

Take care.