TVs use a range of 16-235 while PCs use a range of 0-255. This is why RGB full and RGB Limited are available.
Videos such as movies or TV Shows use a range of 16-235, where PC games use a range of 0-255. It is suggested to leave your settings at Limited (16-235) when streaming/playing movies or TV Shows, which is what most of us do with the Shield in the first place (at least here in this thread). However, when Playing games, the RGB setting will convert to 0-255 as suggested. If not then you will lose shadow detail and washed out high lights, as the case (from a video perspective) when I was playing around with RGB Settings while watching a scene from Game of Thrones. In Full, there was a set of trees in the background that looked more like a glob of green and black. When I set RGB to Limited, those same trees were more detailed and I could see branches and shadow detail as a result.
So again as stated in an earlier post, bt2020 and rec709 are configured as a preference, but with RGB limited and full, Limited is the preferred setting. BT2020 is meant for 4K while 709 is what pretty much everything in the video realm. Also, it is suggested that all components have the same settings. One cannot be set to 709, another to 2020, or one set to Limited, while another is set to Full.
Marantz SR7010/Marantz MM7025
Oppo UDP-203 - Nvidia Shield
Klipsch RP-260f - RP-440C - RP140sa- RP-160m - RB10 - Sony SA-WM500