Do certain jobs require a certain amount of PIC time? Do FAA ratings? Why does the military keep track of it?
as an example, here's what Southwest says about PIC time ...
Flight Experience:
2,500 hours total or 1,500 hours turbine total. Additionally, a minimum of 1,000 hours in Turbine aircraft as the Pilot in command3, as defined below is required. Southwest considers only Pilot time in fixed wing aircraft. This specifically excludes simulator, helicopter, WSO, RIO, FE, NAV, EWO etc. NO other time is counted.
Southwest Airlines defines "Pilot in Command" for the purposes of application for employment as the Pilot ultimately responsible for the operation and safety of the aircraft during flight. The Pilot in Command should also be the Pilot who signed for the aircraft and who is the ultimate authority for the operation of that flight. For military personnel, Southwest Airlines will allow flight time logged as "Pilot In Command" (PIC) only if you are the Captain/Aircraft Commander, Evaluator, or Instructor Pilot. Primary time will only be considered PIC on a specific aircraft after an individual upgrades to Aircraft Commander in the appropriate aircraft. Time logged, as "Other Time" will not be considered.
reference