How to get popular post tags

I need to get post popular tags. Here what I found from http://ift.tt/1MVBmsj

$tag = wp_tag_cloud( 'smallest=8&largest=22&number=2&orderby=count&format=array' );

Here is an example from Wordpress site:

Cloud displayed under Popular Tags title

<?php if ( function_exists( 'wp_tag_cloud' ) ) : ?>    
<h2>Popular Tags</h2>
<ul>
<li><?php wp_tag_cloud( 'smallest=8&largest=22' ); ?></li>
</ul>    
<?php endif; ?>

I did not understand this parameters meaning smallest=8&largest=22 and does this example what I need?

via Chebli Mohamed