Trades are only triggered when profit is > fees. Depending on the market there can be fairly large opportunities popping up (on the thousands) a few times an hour. In a triangle, you only need 1 of the 3 pairs to have an inefficiency in the book to trigger a trade.

During the december craze: very profitable. Now: better than not trading.

If I were american and had to pay higher taxes on short term gains, it would probably not be worth it.