why type $this = $(this) in jquery
<p>I'm new to jQuery and have noticed someone go:</p>

<pre><code>var $this = $(this);
</code></pre>

<p>Why do this? Is it to save typing? Does it help performance? Is it fairly standard practice?</p>

<p>Also I've started doing things such as:</p>

<pre><code>var minus_button = $('#minus_button');
</code></pre>

<p>Should this instead be <code>var $minus_button = $('#minus_button');</code> to signal it's a jquery object?</p>

<p>I read <a href="http://docs.jquery.com/JQuery_Core_Style_Guidelines" rel="nofollow">http://docs.jquery.com/JQuery_Core_Style_Guidelines</a> but couldn't find any suggestions.</p>
