By purchasing a call option instead of ETH, you are taking advantage of leverage; allowing you to use less money to gain positive exposure to ETH rather than using more money to purchase ETH directly.
You can profit if Ethereum price rises, without taking on all of the downside risk that would result from owning ETH. Your losses are limited to only what you paid for the call versus the potentially larger losses equaling the total decline in ETH price had you just bought ETH directly.
If ETH price remains even, you lose some (or all) of the premium you paid for the call. Then you can decide to sell the call for a loss. However, if ETH price goes higher, you profit from the increase. Then you have to decide whether you want to exercise your right to buy ETH at the lower price or just sell the call and collect your profit.
Let’s assume ETH is currently trading for $200. You would like to buy 200 ETH. You could buy 200 ETH and have $40,000 of risk in the market. Or, you could buy 200 ETH calls with a $200 strike price for $9.00 and have a similar exposure but do so with only $1,800 ($9 X 200 = $1,800).
By purchasing the cal you are saying that by expiration you anticipate ETH to have risen above the break-even point: $209, $200 strike price + $9.00 (the option premium paid). The profit potential is unlimited as ETH price continues to rise above $209. The risk for the call purchase is limited entirely to the total premium paid, $1,800, no matter how low ETH price declines.
Before expiration, if the call purchase becomes profitable you are free to exercise the right to buy ETH at $200 or to sell the option to realize the gain. On the other hand, if your bullish outlook proves incorrect, the call might be sold to realize a loss less than the maximum.