In the previous examples I’ve accomplished the same tasks (logging in and logging out) using cookies and sessions. Obviously, both are easy to use in PHP, but the true question is when to use one or the other.
Sessions have the following advantages over cookies:
They are generally more secure (because the data is being retained on the server).
They allow for more data to be stored.
They can be used without cookies.
Whereas cookies have the following advantages over sessions:
They are easier to program.
They require less of the server.