In game framerate limiter is generally less input latency than using driver level Nvidia/AMD or RTSS. In game frame rate limiter can regulate by source but external limiters intercept by frames and cause skipping.
I know you can edit user config file prior to loading DT, %APPDATA%\Fatshark\Darktide\user_settings.config and set nv_framerate_cap
But slider is convenient when people test/tweak their FPS cap balance vs graphic quality without having to restart.