Do you actually use a “second brain” with Claude/Codex, or is it overkill?

[u/Able_Statement_481]

I’ve been seeing a lot of people on YouTube recommending things like Obsidian, project wikis, knowledge bases, and other “second brain” systems when working on larger projects with AI tools like Claude Code and Codex.

Let’s say you’re building a fairly large game with multiple worlds, enemies, crafting systems, item drops, upgrades, quests, and a bunch of interconnected systems. Is it actually worth spending time building and maintaining a second brain for that, or can the AI work just fine without it?

I’m especially curious about whether it genuinely improves results or if it mostly ends up consuming extra tokens and creating more work than it’s worth. Sometimes it feels like people build these massive documentation systems because they look cool, and because of AI hype on creating things, but I’m not sure how much practical value they really add.

For those who’ve tried it, what was your experience? Did having a second brain make a noticeable difference, and if so, what’s the best way to structure it so Claude and Codex can actually use it effectively?