The goal is to be able to notify attorneys in real time that they are needed in a certain courtroom. The hope is that this can eventually be done through push notifications on iOS and Android (fingers crossed), but for now it would be good if the rest of the attorneys knew to look out for him or her without checking the comments on an individual card.
@mentioning someone will generate a notification for the person mentioned (They'll get a "you were mentioned on ..." notification)
It will also generate a notification for everyone assigned to the card (They'll get a "someone commented on the card" notification)
Until there are push notifications, folks can set their notification emails setting to "Instantly" at https://trello.com/my/account ... then they should get an email very soon after the @mention or comment.