People who want to buy large amounts of bitcoin or don't have any access to credit or debit cards will probably look for buying Bitcoins with their bank account. Since there's substantially less risk involved for exchanges when people purchase Bitcoins with their bank account, the fees for such a process are significantly lower. Unlike credit cards, Bank transfers are considered irreversible and reduce the risk of chargeback. So if you'd buy $1000 from Coinbase via a bank transfer you'd pay $14.9 in fees, while if you bought the same amount with a credit card you'd pay $39.9 in fees. As you can see, you can save 50% and more when using a wire transfer. Also, buying limits are much higher when using a bank transfer to fund your account than when using a credit or debit card. On the downside, bank transfers are usually less convenient to execute and take a longer amount of time to process since the transfer needs to clear several banks on its way to the exchange.