It works great until it stops doing anything. I use it on new projects and it makes everything go smoothly at the start and, I think, for much longer.

I haven't done it for existing projects but I have done something similar for an unfamiliar, old and challenging codebase. I worked with the cursor chat agent to produce a document I called architecture.md mapping out high level features to files/classes/functions. This was excellent because I found the document useful and it also made cursor more effective.