The great benefit of experts over I-just-learned-this authors is that experts know how design x or feature y relates to other designs and features not implement

The great benefit of experts over I-just-learned-this authors is that experts know how design x or feature y relates to other designs and features not implemented in the given project. In other words, they know a lot more context and can tell whether something that appears totally normal in the project is actually done in an unusual way that has limitations, etc.