a. They are simple to use.
b. Light in size, thus occupy less memory.
c. Stores server information on client side
d. Data need not to be sent back to server.
e. Cookies persist for much longer period of time than a session.
a. Since they are stored on the client side in plain text, they are not secure.
b. Number of cookies that can be stored and their size is limited.
c. They don't work if security level is set too high in browser.
d. Some people might just disable cookies on their browsers.