Optimizing system for installed software
During the &quot;optimizing&quot; stage, the system is &quot;prebinding&quot; executables. As per Wikipedia:

Prebinding is a method for reducing the time it takes to launch executables in the Mach-O file format.
Prebinding looks up memory addresses of symbols in libraries that the program is using before the program is launched, and stores this information ahead-of-time, so that the computer need not look up (bind) addresses on each launch.