If you've been running The Witcher 3: Wild Hunt on an Nvidia GPU, you may have been experiencing fairly frequent crashes relating to your graphics card's Nvidia drivers.
You'll be happy to know that fans of the game have tracked down the crashes to the "Nvidia Streamer Service", which is a part of the Nvidia GeForce experience. Nvidia's streaming service has a tendency to crash games, including The Witcher 3 and Grand Theft Auto V.
Fans have discovered that the service, which is only used for streaming games to SHIELD devices, is actually causing framerate issues and crashes. The Witcher 3 fan TheRaidenPT has put together a small guide on how to disable the service:
To turn this unnecessary service completely off and regain your lost framerate, as well as prevent any associated crashes, click on the Start Button on the Windows taskbar, search for "Services" and then right-click on its icon and select "Run as administrator".
After that, scroll down through the "Services (Local)" list, find and right-click on "NVIDIA Streamer Service", then select "Properties". First click on "Stop" to turn the service off and then select "Startup type: Disabled" from the drop-down menu.
Doing so should fix some of your framerate problems and prevent crashes, so definitely do it.
You may also wish to set your VSync to "Off", Display Mode to "Fullscreen" and Maximum Frames Per Second "Unlimited".