When someone emails you a PowerPoint presentation, PowerPoint remembers the screen size that was last used. If that version was created on a small laptop, the slides will show up as tiny rectangles on a big desktop monitor.
All the time I see people making edits to presentations in tiny tiles. Why not give your eyes a break and scale up the slide to fit the page? Getting rid of toolbars, the speaker notes field, and reducing the outline on the left will deliver some more screen real estate.