Say you want to buy a gift for about $50. Then you see something you like for $55 or $65. You buy it anyway, especially if you have no more time for shopping.
By giving a gift card instead, you’ll spend exactly what you intended, and the person who receives it can spend it on exactly what they want.
Sites such as GiftCardGranny.com and PlasticJungle.com sell gift cards from popular retailers with discounts on the face value. You could save even more by buying the card from one of them.