A practical scenario where the document matters.
If you're stopped at a checkpoint in a country where officers don't read your home license's language, an IDP gives them an immediate, standardized reference for your license details without requiring an on-the-spot translation. This can meaningfully shorten what might otherwise be a confusing roadside interaction.
Keeping both documents together and easily accessible, rather than buried in luggage, makes any roadside interaction go more smoothly.