One more place to look for causes of file bloat is on the slide masters. If you have cleaned up everything you can think of, but the file is still much larger than you think it should be, look at each of the masters. There may be something included which shouldn't be.
Sometimes, a graphic will be placed on the slide or title master. Since this picture shows on each slide, you would expect the file size to grow with each slide added. Luckily, this doesn't happen. The file will grow with the first slide added, but after that, PowerPoint keeps using the same copy of the image and adds a link to the image location within the file. However, if that graphic is severely oversized, it will still increase the size of the file unnecessarily.
As Bryan learned, the same is not true of backgrounds on the masters such as the handout and notes master. Objects placed on the other masters are just like objects placed on individual slides. They are independent objects.
One of Bryan's files had a case of file bloat with no cause he could find. He went to the slide, title and notes masters: nothing there. Finally, he looked at the handout master. Bingo! Someone had placed a large copy of the company logo on the handout master as a background. Deleting the graphic from the handout master shrunk the file size to where he expected it to be.