The measure is the length of a line of type. To a reader’s eye, long or short lines can be tiring and distracting. A long measure disrupts the rhythm because the reader has a hard time locating the next line of type. The only time a narrow measure is acceptable is with a small amount of text. For optimum readability you want the measure to be between 40-80 characters, including spaces.
Hang quotes in the margin of the body of text. By not doing so a quotation mark that is flush with the text will interrupt the left margin and disrupt the rhythm of the reader. Hanging quotes keeps the left alignment intact and balanced therefore increasing readability.
