They aren’t using it to complete a trade across it. You use it to send information about what is happening in, say, NY to trade locally in Tokyo or São Paulo before anyone else knows what happened in NYC and adjusts their own trading strategy.

You basically are arbitraging people’s access to information.

They’ve been doing this from NY to Chicago (using higher throughput) radio links for a while. See flash boys.

But if you have sophisticated algorithms moving fast enough in NY to only send the information that is worth trading on, this sounds compelling.

I tend to have a dim view of HFTs - I think they’re more or less just stealing pennies from lots of folks while pretending that’s liquidity, but I’m not an expert.