A driver allows games to interface with the graphics hardware, enabling accelerated performance for example. This “app” provides additional functionality on top of that (I don’t know what, but GeForce Experience it replaces provided things like recording gameplay videos etc.) which is not strictly required and, it seems, hurts gaming performance.

As for getting the latest drivers, you can do it manually by going to nVidia’s website and download them, or rely on Windows update to give you reasonably recent drivers.