What are the disadvantages of a debit card?

You need enough money in your bank account to cover each purchase.
Since you paid for the purchase at checkout and the money is out of your account, you have less protection if something goes wrong with the purchase. Your bank won't put money back into your account for items that are never delivered, don't work or were misrepresented.
You may have bank fees—such as monthly service charges, per-transaction costs or penalties—for dropping below your required minimum balance. Check with your bank to find out those extra costs.
You have less protection if your debit card is lost or misused than with a credit card.