It does for non technical users or someone who wants to do a one off transcode job. Most people wouldn't be comfortable using FFmpeg in the command line.

And for the people who are comfortable with that, this provide some convenience in not having to look up command(something I always do) but its never meant to be a replacement for hardcore FFmpeg users

No need to manually install anything and sandboxing. Honestly if I had a suspicious video file I might prefer the browser option so that an ffmpeg exploit would not have access to my machine.