Limiting line length to prevent reader exhaustion:
Note how you feel when you look at the lines of text in the "before" view compared with the way you feel when you look at the lines of text in the "after" view. In the “before” view the lines of text are very long and hard to follow. In the “after" view, the compact line length is much easier to read.
Limiting the line length by breaking up lines of text can prevent reader exhaustion and loss of engagement. Sixty characters per line is optimal for print. Web design experts say fifty characters per line is optimal for the web. If text is enlarged, a twenty character line is best.
Terry's Tips
Since learning this, I have reduced the amount of text on the screen and in print. Now, they seem to be reading the text I provide!
For more information, see Stephen Kosslyn's Clear and to the Point: 8 Psychological Principles for Compelling PowerPoint Presentations