A recent update for The Witcher 3 was supposed to improve performance on PlayStation, Xbox, and PC, but the latter is actually running worse.
The Witcher 3 saw the arrival of patch 4.01 earlier this week, noting that it "improves the overall stability and performance of the game on next-gen consoles and PC, and brings various fixes to all platforms." Only problem is, as reported by Rock Paper Shotgun, that just isn't the case on PC. Upon booting up the game to test out the new settings, RPS found that if you don't have ray-tracing enabled, the game actually runs worse than before.
One of the PC-specific additions added with this update is that a performance mode for ray-traced global illumination is now available as an option, hardware permitted. This setting "improves frame rate by prioritising performance over range and precision," which apparently works well. But without any RT settings turned on, frame rates can dip lower than 25fps, making for a not particularly smooth experience (as demonstrated here).