Screen capturing animations from eevee-viewport

I do not have much experience with rendering animations. what I am wondering is, why is it possible to play a animations in near real time in the viewport, but rendering takes much longer.
I guess it is because for each frame blender has to reload some modifiers, particle groups…
So isn’t the fastest way to render a animation, to use a screen capture software for the viewport render?

With Eevee, play animation in Viewport run at 1 sample per frame. In addition to Eevee viewport there are some tricks that reduce quality for the benefit of speed.
If you want to get a Render output similar to viewport animation, in properties panel, render tab > Sampling set 1 for viewport. In viewport set View to Camera View (numpad 0). In header viewport bar, you disable the “Show Overlays” button. In header viewport bar you find “View” menu and you choose “Viewport render animation”.

Set viewport sampling = 1 is to get a similar viewport play animation speed, but chances are you get a lot of flickering. Increasing samples will improve quality and probably still faster than Final Render Animation.