Joe Gollner of Gnostyx Research covers several real-life case studies in which electronic documents needed to be delivered in alternate ways. Most of us have a consumer point of view regarding the convenience and attractions of tablet devices like the iPad. There are many scenarios, from military to remote construction "off-the-grid" in which alternate deliver (e.g. B/W or grayscale) can work better.
One typical example is that bright, colorful, backlight LED eReaders can destroy night vision for military team members or repair crews that work on night on wind generators. Review this content for an eye opening look at why black-and-white, vector art, gray scale, and yes, even PDF, can sometimes work better than "more engaging" full color content.