There was a video on this site a while ago, I don't know where it is, but it was one of the beat writers getting a mock combine interview with Decosta. Its a really interesting watch if you can find it.
Basically the interviews serve two purposes: (1) to gather some basic background information about the person, and (2) to evaluate the players temperament. I think the second one is probably the more important purpose as teams gather a ton of the background information beforehand (Scouts are out visiting high school coaches, college coaches, looking for all kinds of deep, borderline creepy information about these kids). It's really important to know a player's temperament because of its connection to things like suspensions, emotional responses to adversity in the game and even small things like drive killing penalties. If a player can't hold himself together during an interview where they should know everything that is at stake, that should definitely affect their draft stock because of how important it is to stay poised and focused in football games.
It's not even just a Ravens thing either, there's always stories about weird questions meant to upset the player or catch them offguard- such as the infamous question to Dez Bryant about his mother.
