How much space will you save? That varies dramatically. In my tests, the program shrunk files from nearly 25% nearly 84%, which are substantial reductions. PPTMinimizer leaves your original files intact, and saves the shrunk files as copies. The program is exceptionally easy to use--select the files you want to shrink, tell the program to shrink them, and you're done. Better yet, it integrates with Outlook, Word, PowerPoint, and Windows Explorer, so you can shrink them from directly within applications.
Be aware that this demo version is only good for shrinking files 12 times if you register, and five times if you don't. As to whether it's worth it for you to pay after that, it will depend on how important hard disk space is to you. If you've got a large hard disk, and have no problems sending large files via email, it probably won't be worth your while. But if disk space is at a premium, or if you have problems sending large files, it may be worth the money.