All is well and good if the company will back the pilot if all is going well and the pilot says "look guys, its been a hard week and I need a bit of extra time off."
Ive seen it happen and the pilots are happy to go to the boss and ask. Other companies will not pay properly, thus putting financial strains on the pilot and posssiblely his family. He / she tends to take risks including flying while fatigued.
On the other side of the coin, the fatigue management controls which some companies have put into place invlove some on duty sleeping and structured rest periods.