What is the Proper Usage of $_SESSION in PHP
<p><strong>According to <a href="http://www.php.net/manual/en/intro.session.php" rel="nofollow">php website</a>, session support in PHP consists of a way to preserve certain data across subsequent accesses.</strong> This enables you to build more customized applications and increase the appeal of your web site. A visitor accessing your web site is assigned a unique id, the so-called session id. This is either stored in a cookie on the user side or is propagated in the URL. The session support allows you to register arbitrary numbers of variables to be preserved across requests.</p>

<p>Tapping onto the experience of programmers here, I would like to know what are the <strong>things that should be stored</strong> in <code>$_SESSION</code> and what are the <strong>things that should not</strong>. Example, is it a good idea to store data in a session to avoid repeated queries on the database?</p>
