The headrest can be used up or down. When the headrest is up, the carrier is approximately 3" taller than the regular body size. The headrest is great if you plan on using your BabyHawk with a newborn or if you like having your baby sleep on your back often -- it will give him proper head support.
Most older babies would rather be able to see out easily and have their arms out of the top of the carrier, which is easily done by flipping down the headrest or going for a Custom BabyHawk and choosing a ToddlerHawk.