Chat room description and tags may only be useful a first couple of times you come by a chat room. After that, they are just wasting space. To hide them from the view, you can install the following userscript:

// ==UserScript==
// @name        Hide chat room description and tags
// @namespace   maidcafe
// @match        *://chat.stackexchange.com/*
// @match        *://chat.stackoverflow.com/*
// @match        *://chat.meta.stackexchange.com/*
// @version     1
// @grant       none
// ==/UserScript==

function addGlobalStyle(css) {
  style = document.createElement('style');
  style.innerHTML = css;
  document.head.appendChild(style);
}

addGlobalStyle('#roomdesc, #room-tags {display: none;}');

Or this Stylish script:

@namespace url(http://www.w3.org/1999/xhtml);
@-moz-document domain("chat.stackexchange.com"), domain("chat.stackoverflow.com"), domain("chat.meta.stackexchange.com")
{
  #sidebar #info #roomdesc,
  #sidebar #info #room-tags  {display: none !important;}
}