I'm intrigued. By this, do you mean that, with a PPL, I could legally fly myself to a business meeting (instead of driving), and get my employer to reimburse me just as they would if I'd driven?
Correct. The employer can pay the direct costs of your flight.
How about if I take along three of my colleagues to said meeting?
Essentially, provided they are not
contractually required to travel with you, that's OK. Most of us who do such trips make sure our colleagues are explicitly offered an alternative means of transport.
Public transport and aerial work - exceptions - recovery of direct costs
161(1) Subject to [the usual requirements on aircraft that are hired out], a flight shall be deemed to be a private flight if the only valuable consideration given or promised in respect of the flight or the purpose of the flight other than:
(a) [aircraft hire fees]; or
(b) [normal contributions to group running costs];
is the payment of the whole or part of the direct costs otherwise payable by the pilot
in command by or on behalf of the employer of the pilot in command, or by or on
behalf of a body corporate of which the pilot in command is a director, provided that
neither the pilot in command nor any other person who is carried is legally obliged,
whether under a contract or otherwise, to be carried.