@clintflint - I'm sure it makes a difference when they need to measure rashes and burns and in calculating topical medicines, if not other kinds of medicine. The total surface area of a body probably helps to estimate the total amount of blood vessels and so forth for example.

Hopefully any doctor who is working with a patient where this is a crucial number to know will use a more complex equation to figure it out as there are a number of factors that can make a difference. But if they just want a rough estimate I'm sure the standard formula is fine.