The occasional news stories about secret service agents who face the embarassment of having "lost" a notebook containing top secret material are useful reminders that portability does have a downside. What's easy to carry is also potentially easy to steal. And, while "top-secret" documents might be protected by sophisticated encryption methods, it's still annoying to have to replace the notebook itself.
Toshiba notebooks are equipped with security features to protect your data, such as special passwords, and features to protect the hardware itself, such as a slot for a Kensington cable lock (a steel cable for securing the notebook).