|Whoever said that is mistaken. They might think that improved things but it won't.|
Simply put, if your NIC is set to auto, and the other end is also set to auto and you're showing a 1000 Mbps connection. Manually setting both ends to 1000 Mbps won't change anything......you'll still be connecting at 1000 Mbps.
If you're talking about streaming video from the internet from a site like YouTube, this won't do anything at all since the connection rate for your external connection will be much slower than your LAN connection rate.
There might be tweaks to improve video playback performance but they'll be graphic card tweaks, not network tweaks.