If you have say a post entry:

  .post {
    border: 1px solid #000;
  }

  .post .title {
    font-weight: bold;
  }

And you want to put it into a sidebar

  .sidebar {
    background-color: #ccc;
  }

  .sidebar .title {
    text-decoration: underline;
  }

That post's title is now going to be underlined. That's one of the reasons for namespacing. If the classes were `.post--title` and `.sidebar--title`, this would be avoided