There is often information about a card which you want very visible/obvious by some means other than formatting. For example:

• whether a card is viewable by anyone
• whether a card is used in code (assuming we add something like "+*used in code" — see expose card metadata in cards)
• ??

(Note that what counts as metadata is in the eye of the beholder. Any solution wouldn't really be limited to metadata, it's just the most obvious use case.)