I review most of the code I get LLMs to write and actually I think the main challenge is finding the right chunk size for each task you ask it to do.
As I use it more I gain more intuition about the kinds of problems it can handle on it's, vs those that I need to work on breaking down into smaller pieces before setting it loose.
Without research and planning agents are mostly very expensive and slow to get things done, if they even can. However with the right initial breakdown and specification of the work they are incredibly fast.