You're opening a can of worms here.
PPL as PIC with passengers - No.
PPL as PIC without pax (ferry) - Yes,as self fly hire for example.But then again some voices say no, because the flight is paid for by the customer, i.e. the empty return leg.
CPL as safety can't log PIC.
In some countries AOC work is exempt from fuel tax and only applicable to pilots listed in that AOC.
A PPL as PIC in the techlog would levy a fuel tax on the PPLs flight time.
Techlogs are checked every year by the taxman...
Flight instruction (TR) on an AOC only for employed CPLs, PPL can only train in a TRTO / FTO or whatever the new EASA slang is.
And you can't log copilot time on the little birds.