A Bitcoin (spot or futures) exchange (like any online trading firm) charges its clients a fee to carry out trading activities. As exchanges face the risk of hacking and theft, it is wise not to trust an exchange with all your coins. You should split and keep part of them in other devices or cold storage. Now with bitcoin futures being offered by some of the most prominent marketplaces, investors, traders and speculators are all bound to benefit. These centralized marketplaces will facilitate trade based on a trader’s outlook for bitcoin prices, gain exposure to bitcoin prices or hedge their existing bitcoin positions. Overall, the launching of bitcoin futures by Cboe and CME will facilitate price discovery and price transparency, enable risk-management via a regulated bitcoin product and give a further push to bitcoin as an accepted asset class. (For more, see: The Risks Of Buying Bitcoins.)
When a Fund purchases a put or call option on a futures contract, the Fund pays a premium for the right to sell or purchase the underlying futures contract for a specified price upon exercise at any time during the option period. By writing (selling) a put or call option on a futures contract, a Fund receives a premium in return for granting to the purchaser of the option the right to sell to or buy from the Fund the underlying futures contract for a specified price upon exercise at any time during the option period.
When the Fund has an open futures contract position, it is subject to daily variation margin calls that could be substantial in the event of adverse price movements. If the Fund has insufficient cash to meet daily variation margin requirements, it might need to sell securities at a time when such sales are disadvantageous. Futures markets are highly volatile and the use of or exposure to futures contracts may increase volatility of the Fund’s NAV. Futures contracts are also subject to liquidity risk.
There's a lot of ins and outs which can get confusing in arbitrage trading. We won't go into the technicals of why futures contracts trade at a premium to spot price. You can read a full explanation here. If it's not of interest to you, all you need to know is that there's a tendency, the further out in time the futures contract expires, for the premium to spot to be higher and higher in nominal percentage terms.