falconeasydriver, CRS does not care how you get your days off, bidding for them or for a trip that gives you them is the a same to it.
Bidding for a trip, means that if anyone else gets assigned the specific trip, you lose. Bidding for days off means you allow CRS a way to find you a trip of the many possible ones available.
Rostering is not actually trying to maximise our hours, senior management is trying to get a pint out of a half pint pot, all other systems then try and solve that problem