Cookies are used to store user specific information in form of text strings .A persistent cookie is a cookie which is stored in a cookie file permanently by getting some space on the hard disk of the web browser’s computer. By default, cookies are created as temporary cookies which stored only in the browser’s memory and these cookies are erased as the browser gets closed.
when to use temporary cookies and when to use persistent cookies depends on the requirement.

Persistent cookies are used for tracking long-term information but Persistent cookies are less secure because users can open cookie files see the cookie value

Temporary cookies can not be used for tracking long-term information but Temporary cookies are safer because no programs other than the browser can access them.