They are weak and therefore hardly adequate to their purpose in aiding the understanding through the eye.

Being cast on the upper part of the type body, they leave a blank space below and thus impair the beauty of the line and interfere with good spacing.

Certain rules for the position of quotation marks when used with other marks are based upon these typographical considerations rather than upon logical considerations.
_Rules for the Use of Quotation Marks_ 1.

Every direct quotation should be enclosed in double quotation marks.
"I will go," said he, "if I can." Reports of what another person has said when given in words other than his own are called indirect quotations and take no marks.
He said he would go if he could.
2.

A quotation of several paragraphs requires quotation marks at the beginning of each paragraph, but at the end of the last one only.