Logging hours is not a reward it is simply an administrative reacord keeping task that every pilot is legally required to do.
If however, you agree with someone that if they do a certain task or provide a certain service or provide certain goods and in return you will give them x number of hours flying in an aircraft then the giving of the x number of hours flying is indeed a reward and is valuable consideration.
Thus if a PPL was not being paid for the time they were giving instruction but the club in return permitted them to use the aircraft for their own pleasure at no cost then there is valuable consideration being provided.
This is not to be confused with asking a PPL to fly your aircraft from A to B. In that case, they have not got the use of the aircraft. They are providing a service for you which you do not compensate them for.
Of course, there is one fly i the ointment for all this - the minimum wage. If you employ a person to complete a task they are entitled to the minimum wage. So how does an organisation employ a PPL to complete flight instruction and not pay them. Dammed if you do and dammed if you don't situation!
Regards,
DFC