Somewhat against the common sentiment, I find it's very helpful on a large legacy project. At work, our main product is a very old, very large code base. This means it's difficult to build up a good understanding of it -- documentation is often out of date, or makes assumptions about prior knowledge. Tracking down the team or teams that can help requires being very skilled at navigating a large corporate hierarchy. But at the end of the day, the answers for how the code works is mostly in the code itself, and this is where AI assistance has really been shining for me. It can explore the code base and find and explain patterns and available methods far faster than I can.

My prompts end to be in the pattern of "I am looking to implement <X>. <Detailed description of what I expect X to do.>. Review the code base to find similar examples of how this is currently done, and propose a plan for how to implement this."

These days I'm on Claude Code, and I do that first part in Plan mode, though even a few months ago on earlier, not-as-performant models and tools, I was still finding value with this approach. It's just getting better, as the company is investing in shared skills/tools/plugins/whatever the current terminology is that is specific to various use cases within the code base.

I haven't been writing so much code directly, but I do still very much feel that this is my code. My sessions are very interactive -- I ask the agent to explain decisions, question its plans, review the produced code and often revise it. I find it frees me up to spend more time thinking through and having higher level architecture applied instead of spending frustrating hours hunting down more basic "how does this work" information.

I think it might have been an article by Simon Willison that made the case for there being a way to use AI tooling to make you smarter, or to make you dumber. Point and shoot and blindly accept output makes you dumber -- it places more distance between you and your code base. Using AI tools to automate away a lot of the toil give you energy and time to dive deeper into your code base and develop a stronger mental model of how it works -- it makes you smarter. I keep in mind that at the end of the day, it's my name on the PR, regardless of how much Claude directly created or edited the files.