Each loading animation spends 0.02 seconds per frame if Vsync is enabled. With Vsync disabled, the animation goes as fast as your computer can load the mission, which should be nearly instant. This saves some time over the full run.

This made my game screen completely pitch-black, do you know what might be the cause?

That happens with that version in OpenGL mode. It's a known bug that should be fixed in the latest version that'll come out soon. For now, use Direct3D9 (shader). Change it via the registry files in the WA\Tweaks folder if you can't use the menu.

You want to play with vsync off. Loading animations are faster and rope feels smoother. Just get used with the screen tearing and you're alright. :)

The bug Spec3x reported should now be fixed since the release of version 3.8 earlier this year.