I'm struggling to understand the purpose of this, or why I would choose this over php-fpm. It seems to be competing with Docker as it isolates applications with

I'm struggling to understand the purpose of this, or why I would choose this over php-fpm. It seems to be competing with Docker as it isolates applications with cgroups, but if I'm already running docker, what's the point? Perhaps another layer of isolation? ¯\_(ツ)_/¯