The problem that I see with background agents in general is that not following along and making it interactive adds compounding interest to the cost of editing, reviewing and understanding the agent's output since it's not something I've seen come together firsthand.

Agents also very rarely are truly hands-off: most of my usage is walking through a pre-determined set of steps and course-correcting along the way. In my experience, having it run out of sight leads to heavier editing since smaller realignments couldn't be applied along the way.