Disadvantages of PNG
It would be grand if there were no downsides to using .png, but, alas, there are. Some are more substantial than others.
No Support for Animation
This is a very minor downside. Unlike the .gif file type that supports both still and moving images, .png supports only still images. A sister file type, .mng, for Multiple-image Network Graphic, has been created to replace animated .gifs.
Whenever you use something new in your Web work, you run the risk that you'll lose part of your viewership. Both the current versions of Netscape and Internet Explorer support .png; however, older versions of both browsers and some third party browsers still do not. If your business depends on your image being seen, it's not the time to make a political statement with a .pnggo ahead and use the GIF or JPEG image formats.