For some reason, someone just sent me ten images, but rather than sending me the original scans or jpgs or whatever they had, they send me a PowerPoint file. Why is this bad? Well, first off, you have to jump through some hoops to get images that aren't distorted or have lost resolution.
Apparently though, PowerPoint does have one advantage in that apparently there's a bit of compression. The PowerPoint file is 993 KB, while the 10 jpgs together are 1.38 MB. While the compression is slightly nice, I'm not sure the ~400KB saved is worth the extra work it took me get the images.