It depends on your operator. Am on a 3 man crew for a very busy aircraft and it never works in our favor. Company thinks vacation (we have 2 weeks per year) is covered the 2 other crew members. How is that vacation when the other 2 guys have to work extra to cover? Plus they make us cover other aircraft, but other aircraft pilots never cover us. Needless to say, ours doesn't work terribly well. We try to do 14/7, which many times has been more like 21/7, 25/4.
We joke about negotiating a 7 on, 7 on, 7 on, 7 on schedule.