From the 
Nielsen Norman Group
Evidence-Based User Experience Research, Training, and Consulting
Topics: Visual Design, Intranets
Summary: Related links are often chunked as a set, each with an icon. One bad icon hurts user interaction. A set of bad icons is worse because it amplifies confusion, adds clutter, and wastes screen real estate.
The article predominantly speaks about the use of icons on intranets, but IMHO also applies to anything and any place where icons are used including infographics and courses.
This discussion post is outdated and has been archived. Please use the Community question forums and official documentation for the most current and accurate information.