This is due to the fact that every time the image changes, the background for the logo has to be edited. On the other hand, in the case of the PNG format, the image will float with a faded drop of shadow. This will help make your web fast, simple and dynamic.
The PNG format has the distinct advantage of displaying full colour photographic images and supports a managed color palette. It never degrades in quality and saves the original file information. This quality makes for brighter and crisper images.