<p>They're allowed, <a href="http://meta.stackexchange.com/questions/113658/no-url-shorteners/113660#113660" title="if you can find it, don't hide it">but they're discouraged</a>. </p>

<p>The problem with URL shorteners is that they obfuscate the final destination and prone to breaking, causing linkrot. </p>

<p>When you use the original link instead, it's far easier to track down a replacement link should that page you link to die. When you wrap around a URL shortener, it's a guess if it's porn or not and which video you wanted them to watch.</p>

<p>Better edit in the actual URL being used now when we can still see the redirect instead of waiting for when it's gone and having a hole of nothing to deal with.</p>

<p>Err on the side of being plain and direct, which the shorteners are not.</p>