Unlike disc backups that are throttled by the Blu-ray drive's 9MB/s speed limit, .pkg files run at the full speed of the internal HDD . This results in noticeably quicker song loading in the Rocksmith menus.
You can use the PS3's native "Turn Off" menu feature to batch-install dozens of downloaded song packages at once while the system shuts down, saving you from clicking through each individual installer. Requirements for PKG Installation