The CP wants descents flown during approaches at 3 degrees.
Enroute descents in such aircraft, unpressurised, are done at CA along a more approximate "6 x" profile. Easy to calculate and looks after the punters (ie 8000 feet to descend, start 40 nm out).
The techniques learnt at stage of a pilot's career should help when they "move up". I'm sure there's T&C Pilots out there who pull their hair out when newbies on high performance aircraft can't even derive a simple enroute descent profile through onto an instrument approach...