It will work on sites like Netflix and YouTube (adaptive streaming) that allow streaming in different definitions especially 480p and lower. Don't know about iTunes but Amazon pretty much streams only in higher definition like 720-1080. Because of this the VDS may cause severe buffering if left on while streaming Prime video, not to mention eating through data much quicker
I mainly stream Netflix and have my account there set to lowest definition possible so the VDS doesn't have any effect regardless if on or off.
This explains the difference between progressive and adaptive streaming: http://support.hughesnet.com/faq/internet/progressive-and-adaptive-streaming