Earlier quoted context omitted.
Much cheaper, doesn't need to plug into wall, more and more open viewing options. Question should probably be reversed (says this Apple fanatic).
It still needs power though so it needs to be plugged into something - whether USB or wall socket. What are the open viewing options? It seems to only provide youtube and google movies in countries that don't have netflix. Does it support streaming a local video from a phone or PC?
Not every TV/monitor supports this since there aren't that many devices out in the field that utilize HDMI power, but if your TV does provide power over the HDMI port then the Chromecast can get everything it needs just from the HDMI port.