JPG does save in distribution size though. I could easily see myself doing that.
Why would one want to use lossy jpgs? well, the same reason the whole world uses it as the primary image distribution format
Come to think of it... I'll probably do it too
I have a game that will use big backgrounds and I don't want the distribution getting all huge because of that.
Won't make a difference performance-wise though, except at image load time.