The problem with it being so easy to create great content, is finding material to include that's permitted. With so many files and resources shared throughout the Internet it can be easy to use something that wasn't intended to be.
The Creative Commons (CC) website allows teachers to search through appropriately licensed material, and add icons/badges to self-created material to share. Whether a teacher is creating a slide presentation for the next lesson on fractions, a .pdf document explaining the rock cycle, or a video sharing an example poem, files are often needed to make the content great.
For instance, a teacher might search for images that help to explain how to divide something into thirds. To make it easy to find images that are approved for use in a situation like this, use the CC search page to look through Flickr, Google Images, Fotopedia, or Wikimedia Commons to find what you need. The same process can used for images in a .pdf and videos for a movie.