We probably need to update the movie render dimensions if we want to get animated short reels showing correctly on social media like Instagram.  Therefore, for rendering movies, we would need to include the option 1080 x 1920 size.  The alternative is to render out our images in that dimension but we'd then have to take them into an external video editor to compile them into a movie.

I would say it is preferable and good practice to always render to image sequence, for later processing. It's safer if something bad happens you can easily pick up where you left off.
Having said that, I agree saving directly as a video file can be good anyway for someone who wants to use Poser from start to finish, in short render time cases (consider risk / benefit).