If you want to make your presentation non-modifiable, you save it to *.pdf format or *.ppsx format (PowerPoint Show format - see Automatically show your presentation). However, if you want to publish the presentation on your personal or corporate Web site, the better option is to export slides as separate pictures.

If you plan to create a presentation for your family, friends, or colleagues and have only photos, you don't need to spend hours on inserting and formatting pictures in PowerPoint. Use a relatively new feature Photo Albums that will automatically do all the work for you.

You usually work with only one presentation at a given time. But occasionally, you may need to open two or more presentations at once. E.g., to copy text or slides from one presentation to another.

Sometimes you want to show your presentation on different computer, and that computer does not have same fonts as your PC.
To display properly that presentation, you should embed the fonts in your presentation so that the desired fonts will be available on the other PC.