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.
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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.
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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.
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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.