So, lets say someone breaks in and steals my server over the weekend. The MINUTE they unplug it to steal it, the data drive that contains all my sensitive data will NEVER reveal its contents. They have my computer but I have no breach. Same thing with my laptop, which I take home every night. All data containing PHI is on the encrypted drive, and if I lose it, it is an expensive paperweight for someone.
Not really a paperweight since they reformat them and make 'em as good as new. But it's great that they won't be able to access your data protecting you against any major liability.