How does this work in practice when it takes days to transfer coins and the clearing fees are high still
The last time I did this about a week or 2 ago, there was an 8% difference between GDAX and Bittrex. At the end of it, after fees and all that, I made 6%.
That is, if LTC is higher on exchange A than B, then you buy all you can on B and sell on A. You've made free money, but aren't strictly better than before because you have a different allocation across exchanges. But then you can later do a slow transfer that evens them out.