It's set by most modern games to 1. And you can't go below 1 in NVCP either.
As speculated it's like pre rendered frames setting.
There used to be setting of 0 but that's not available and maybe not even possible for NV cards anymore. Where as AMD has hardware scheduler still and may do a 0.
I couldn't find it tested anywhere and with the again broken AMD drivers I don't blame anyone for not testing it, there are 2060S, 2070S, 5700, 5700XT, 3000 series CPUs to review all in 1-2 weeks because AMD and NV are nuts and have price fix launch at same time at same prices with near identical value.
Again being explained as pre rendered frames:
DX11 only. Lowering the driver delay, aka how much CPU "pre renders" frames for GPU. I bet they set it to 0 and "synced CPU and GPU" instead of having 1-3 frames buffer/pre render, 1 is common but for say CF/SLI one would use even more.