Yes, credit card joints - as in grout joints the thickness of a credit card - are popular, but given tile industry standards, they aren't possible, appropriate, or even recommended.
Many installers have had customers who have seen tile installations in a magazine or brochure which is exactly what they want in their homes. Unfortunately, the “look” they want to achieve with credit card thickness grout joints most likely will not be possible using the tile that has been selected.
Let's explore why.