My last company (household name loco) took the view/were advised to take the view that after a max discretion duty or if the crewmember reported fatigued at the end of a duty accommodation would be provided on the basis of due care. There was never a problem with the max discretion bit as it so seldom occcurred and when it did few wanted anything but their own bed and declined it no matter how tired they were. No one I ever heard of reported fatigued as this would have brought on (percieved) trouble in the follow-up (esp true for cc.)
Thus the protection from legal comeback cost the company absolutely nothing apart from the appearance of giving a concession to aircrew, something they were always extremely reluctant to do.