Many players complain that FPS significantly drops with enabled HairWorks in The Witcher 3: Wild Hunt. To correct this problem, you can use the following solution.
Follow the path «…\The Witcher 3\bin\config\base» and find file called «rendering.ini». Find there line HairWorksAALevel. By default hair smoothing is set on 8х. Set 2 and enjoy the game with +5-10 FPS.
Solution for AMD graphics card
Create a profile for Witcher3.exe in AMD Catalyst Control Center and set the settings as in the screenshot below (It can be used not 8х, but 4х, as at (2x) — hair will look awful.