The order book from the API is at the very minimum delayed (by network and protocol latency if nothing else) and aggregated/sampled (full feed is too big), so a

The order book from the API is at the very minimum delayed (by network and protocol latency if nothing else) and aggregated/sampled (full feed is too big), so an insider can have an advantage of more complete and timely data. That's for honestly run APIs, then an exchange can play some games with that feed if they want to...