The PNG format was developed as a replacement for the GIF format when it appeared that GIF images would be subject to a royalty fee.
PNG graphics have a better compression rate than GIF images which result in smaller images than the same file saved as a GIF. PNG files offer alpha transparency as well as animation.
PNG images, like GIFs, are not well suited to photographs.
It is possible to get around the banding issue that affects photographs saved as GIF files using true colors, but this can result in very large images.
PNG images are also not well supported on older cell phones and feature phones.