I wonder what the class sr-only is? Is it important or can I remove it? Works fine without and no explanation is given in the documentations.

Here's my example:

  <div class="btn-group">
    <button type="button" class="btn btn-info btn-md">Departments</button>
    <button type="button" class="btn btn-info dropdown-toggle btn-md" data-toggle="dropdown">
      <span class="caret"></span>
      <span class="sr-only">Toggle Dropdown</span>
    </button>
    <ul class="dropdown-menu" role="menu">
      <li><a href="#">Sales</a></li>
      <li><a href="#">Technical</a></li>
      <li class="divider"></li>
      <li><a href="#">Show all</a></li>
    </ul>
  </div>