The Application Process

I mentor someone applying to business school who has a DUI on his record. Clearly he will need to mention it wherever a school might ask about convictions, but he was wondering whether it would be a good or bad idea to write about the situation in more detail, including what it cost him personally and what he learned, in the additional information/essays area. Is it better to say the least possible and only say more if asked or give a more complete explanation?