I mentioned coding as a use case in my comment you replied to. You were asking for an example for when one wouldn't use vector search and I provided one. I did not say similarity search would be a substitute. I said that for the coding case you do not need it.

>you would still likely want to build a similarity search engine

In practice tools like Claude Code, Codex, Gemini, Kimi Code, etc are getting away with searching for code with grep / find and understanding code by loading a sufficient amount of code into the context window. It is sufficient to understand higher level concepts in the code. The extra complexity of maintaining vector database top of this is not free and requires extra complexity.