The System 7.5 Update 2.0 contains additional files or updates that enhance your computers stability. PCI-based Power Macintosh computers shipped with system software 7.5.3, it is not necessary to install the update. The System 7.5 Update 2.0 has a few components that are newer than the versions included with system 7.5.3 that shipped with your CPU. The three software updates include Drive Setup update, Apple Guide update, and an Ethernet Compatibility extension. These updates are included in a folder called 'Important Software Updates' on the hard drive of the PCI-based Power Macintosh computer.
The Tech Info Library article titled "System 7.5 Update 2.0: Important Software Updates ReadMe" contains more information that can help you decide if you need to install these updates.