I would very much like to be able to tell individual dwarves what work they should do, what work they can do, and what work they shouldn't do at all. A system where each post in the [p]referances - [l]abor could be set from 1(black) to 5(white) where the highest available job is taken, or maybe, with less chance, the next highest.
This would be perfect for such dwarves as the butchering Butcher, who can haul whenever no fresh dead animal is nearby, the tanner.
All haulers could be set to haul food before anything else, thus minimizing rotten newly bought food at the trade depot. Fisherdwarves could be set to clean fish whenever possible. Farmers could do other (less important) jobs at winter. The list goes on.
Another, related topic is that of what tree goes down and where do the miners dig. I often want to dig out small rooms and my miners are set to only mine. The consequence is that they afterwards get no job-lazy. The ability to say: "This area should be dug out asap, and that whenever no more important work is available."