I found it depends very much on the task. For "architect" sessions you need as much context as you can reasonably gather. The more the merrier. At least gemini2

I found it depends very much on the task. For "architect" sessions you need as much context as you can reasonably gather. The more the merrier. At least gemini2.5 pro will gather the needed context from many files and it really does make a difference when you can give it a lot of it. On coding you need to aggressively prune it, and only give minimum adjacent context, or it'll start going on useless tangents. And if you get stuck just refresh and start from 0, changing what is included. It's often faster than "arguing" with the LLM in multi-step sessions. (the above is for existing codebases. for vibe-coding one-off scripts, just go with the vibes, sometimes it works surprisingly well from a quick 2-3 lines prompt)