Hi,
The Intel(R) Itanium(R) Architecture Software Developer's Manual Revision 2.2(http://download.intel.com/design/Itanium/manuals/24531705.pdf) will provide the answers to your questions. Please see chapter 4 (section 4.2 "Predication") starting at page 1:163. It talks about when to use branches and when to use predication. If you have any further questions after reading this chapter, do let us know.
Regards,
Kalyan Muthukumar