Tax arbitrage.

Suppose Bob got some bitcoins in 2010, he lives in the USA and wants to use his bitcoins for daily expenses, but he doesn’t want a massive tax penalty. He can use loan shark to borrow against his “old bitcoins” to obtain “fresh bitcoins” for daily expenses.

This idea relies on the fact that bitcoins obtained recently, close to the current price, appreciated less than bitcoins obtained when bitcoin’s price was low, and therefore, at least in the USA, you don’t have to pay as much in capital gains taxes when you spend them. Bob just has to put up some of his “old bitcoins” as collateral and then he gets some “new bitcoins” from the lender.

Bob does well if the interest rate he pays on his loan is lower than the capital gains tax he would owe if he spent his “old bitcoins.” The lender does well too, because she just gives Bob some bitcoins (perhaps she lives in a jurisdiction that doesn’t charge capital gains taxes on bitcoin) and then later she gets back the same amount plus interest, or, if Bob doesn’t pay off his loan on time, she gets his collateral, which is more than she was owed anyway.