That could be useful for arbitrage, assuming both exchanges had instant transactions activated.
Problem of course is conversion back to btc (or whatever coin), so it wouldn't necessarily be equal value. It depends on if the conversion + trading fees is less than the btc fees when sending.
But yeah, could be useful, in the same way doge is... lots of folks use doge to send between exchanges just due to the low fees involved. However then it also depends on what fees exchanges charge to send dash.
Taking advantage of arbitrage opportunities would be the perfect use case for this tech. You wouldn’t have to worry about changes in value because the transfer between exchanges would be instantaneous. Unless of course one exchange had a wildly different value, which doesn’t happen often, and maybe then Dash would be the target of the arbitrage...