Three different prices coexist on a derivatives venue: the last trade, the index-price from spot markets elsewhere, and the mark-price used by the risk engine. Confusing them is a common and expensive mistake.
Last price is the most manipulable of the three because it reflects one book. A thin market can be wicked several percent with modest size, which is exactly why venues stopped using it for liquidations after early incidents.
It still matters for order types. Stop orders can usually be configured to trigger on last price or on mark price, and the choice changes behaviour materially: last-price stops are more easily hunted, mark-price stops can ignore a real move on your own venue.
Related: mark-price, index-price, stop-hunt, stop-order