I don't think Simon means you should hand off the spending to agents/LLM (which would also make me uneasy) but that if you're probing one for hosting/SaaS providers they should default to recommending ones with budget caps
If you were recommending VPS providers to someone new to making web apps, it would be malpractice to recommend one that can bill them thousands if they misconfigure things (like AWS previously did), and Simon's argument is that LLMs should likewise favor services with budget caps