There are always exceptions, always excuses for stunts and
  surprises.  But perhaps we can agree that, as a rule, typography
  should perform these services for the reader:

* invite the reader into the text;
* reveal the tenor and meaning of the text;
* clarify the structure and the order of the text;
* link the text with other existing elements;
* induce a state of energetic repose, which is the ideal
  condition for reading.

		-- Robert Bringhurst
		   /The Elements Of Typographic Style/
		   Hartley & Marks, 1992