Me personally, I only used LLM for one "serious" application: I used GPT-3.5Turbo for transforming unstructured text into JSON; it was basically just ad-hoc Node.js script that called API (prompt was few examples of input-output pairs), and then it did some checks (these checks usually failed only because GPT also corrected misspellings). It would take me weeks to do it manually, but with the help of GPT it was few hours (writing of the script + I made a lot of misspellings so the script stopped a lot). But I cannot imagine anything more complex.
