Serif typefaces are traditionally used in print for the main text. As was already said above, the notches help keep the line, and his eyes less tired.
For the withdrawal of the text on the screen, you can use a sans serif font, but decided to increase the line spacing distance. The meaning of this action is the same — to help the eye to keep the line, to visually separate them.
The titles often make the contrast design to the main text, i.e. if text is typed in a sans serif font, the title is type a serif font and Vice versa.
The source code issue is always very horrible about any printing to the value of that speech, as a rule, is not; use both the font family in about equal measure.