Imagine how many people show their presentations on a laptop. Some people have a screen on their desk and show it on that. For an event, the people will be using a digital projector, and that’s a really big screen. But the resolution used in these situations is actually not very different, and you are probably using the wrong resolution, even projected four metres wide.
The average screen resolution on a laptop is 1024 x 768 pixels. This is also true of most mid range projectors. On a 15″ screen, that works out to 96 dpi. This means that even if you import a 300 dpi image into your PowerPoint, your screen can only effectively show a 96 dpi representation of it. That’s a lot of wasted data and processing power.