Here is a breakdown of Content Protection
If content protection is turned on, BlackBerry device content is always protected with the 256-bit AES encryption algorithm. Content protection of BlackBerry device user data is designed to
-use 256-bit AES to encrypt stored data when the BlackBerry device is locked
-use an ECC public key to encrypt data that the BlackBerry device receives when it is locked
Strong: 160-bit ECC public key; provides good security and good performance, adequate for most situations
Stronger: 283-bit ECC public key; provides better security but slower performance than the Strong setting
Strongest: 571-bit ECC public key; provides the highest level of security but the slowest performance of the three settings
Security Wipe & Content Protection
The BlackBerry device wipe process is designed to delete all data in memory and overwrite memory with zeroes. If content protection is turned on, the BlackBerry device also uses a memory scrub process to overwrite the BlackBerry device flash memory file system. The BlackBerry memory scrub process complies with United States government requirements for clearing sensitive user data, including Department of Defense directive 5220.22-M and National Institute of Standards and Technology Special Publication 800-88.
Generally, it is there to provide the level of data security that the most sensitive companies require.
The US Government requires this kind of security for their data as one example. They probably add smart cards as well. Security Technical Overview