PDR, the difference is that there is a legal number of hours a pilot may fly as a crew member (flight hours) and be on duty (flying, standby, being positioned around country/world).
There are 7 day limits, 14. 28, monthly , yearly limits etc.
A bit like an HGV driver can only do so much before he/she must pull over for a rest of a minimum duration. Any HGV driver found to be driving with the tachometer disconnected gets in serious trouble. An employer bound by flight time limitations has a responsibility, as well as the crew member to jointly ensure these limits are not exceeded.
I think that was the question you were asking ?
