@mena Please don't hijack the original post. But to answer your question, most likely it will also protect the USB devices connected to it from power surges. These USB ports are meant to power or charge devices only and does not have data communication capabilities. USB devices such as USB keyboard/mouse, USB game controllers, etc will require both power and data and therefore have to be connected to the RPI USB ports and draw power from it as well.
@jay81uk simonster is right about the power requirements of various RPi models. So what is yours?
The Kindle Fire power supply normally will provide 1A current which 150ma more than the one from chromecast.