PBI CE = ProBook Installer Clover Edition (
http://www.tonymacx86.com/hp-probook-yosemite/128774-hp-probook-installer-clover-edition.html).
In PBI CE you will selected whether or not to install latest version of Clover, specify what HP ProBook/EliteBook model you have for kext installation and DSDT.aml patching (need to have pressed F4 at Clover Screen to have a clean DSDT.aml to patch) and any other tools you want to install.
Without a patched DSDT, you won't be able to use all of the features of the ProBook/EliteBook, such as audio, HDMI, networking, etc.
-bth