Hair that is "built-up", or wrapped somehow in the crown area is going to give height to the wearer. It also alleviates flaws such as flat heads, thick or undefined chin lines. This look elongates a short round face. No worries girls, for it looks good on those of you without any flaws. Just not a good idea for tall ladies or those with thin, long faces or sharp chins. The latter can have an updo certainly, just no braids, curls, twists or anything specifically in the crown area that will cause accentuation to problems areas rather than draw attention away from them.
As I said, perfect oval faces can wear hair either way. However, updos that concentrate their artwork on the back of the head rather than the crown will better suit those ladies who possess sharp and/or long features.
Keep checking back for prom pictures, ideas and tips for how you can fashion your prom hairdo.