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;}
    }