When I create PNG files with very small disk size, I tend to wonder if the file size becomes less important than the time viewers would need to decompress the image. Technically that would be trivial too, but I've wondered about it for a long time. We all know that more-compressed PNG images take longer to compress, but do they take longer to decompress?
I don't know if this information affects the question, but I am wondering about this in relation to both icon-type files (which are small because they contain few pixels) and huge line-art files (which are small because they compress their pixels very effectively).
EDIT: In response to the answers I've been getting, I want to note that this is not strictly a network issue. Windows users might not notice this, but most icons used by the desktop environment are stored with PNG compression, and dozens of them need to be rendered when the system starts. The huge line-art that I referred to was mostly desktop wallpapers like the ones at http://simpledesktops.com/, but various posters, videogame resources, and other things could also fit that description.