Information architecture is equal parts art and science. Whether you hire a dedicated IA professional, or just sort of let IA happen on your projects, if you’re designing things with content, you’re using IA.
But while you can just kind of “let the content happen,” in whatever way seems to make sense for your project at the time, a well-thought-out, well organized structure for your content can make your site infinitely more usable for your end users.
While not every project can have a dedicated IA, understanding the basic principles behind good information architecture can go a long way toward making sure your site’s content is as easy to access and use as possible.