Their fees for cryptocurrency are small (between 1.5% - 2.5% depending on amounts, higher amounts have a lower fee), but they take it on both the buying and selling end. So if the amounts you're moving require a 1.8% fee, then for both buying and selling you end up with 3.6% in fees. Coinbase and most other CEXes charge this and they claim part of the fee is due to instability in the price, so this fee acts as a spread they can use to not lose money.