I'm in the "no such thing" category, mostly.
All new arrivals are drafted into the "Hauler" corps. They handle butchering, tanning, fish cleaning, pump operation, block production and construction masonry, stone smoothing (but not engraving), herbalism, wood cutting, animal training, milking, shearing, and sand/clay collection. Some fiddling is needed to exclude them from "production" masonry shops and "production" glass furnaces, but not too much. I turn off smoothing once I get someone I designate for engraving, and switch haulers on when I need a massive smoothed area in a hurry.
Skilled migrants (Where 'skilled' means 'skill I need or want more of') are removed from the Hauler corps and assigned to their specialist duties. Very rarely is there overlap, except for 'farmer' type duties, which are handled by one class of worker (farm workers), and include the milling/brewing/farming tasks. Specialists do not haul. Haulers do not specialize.
Combat migrants (those designated for combat tasks) are haulers when off duty, and always carry their military equipment. All combat migrants are given a labor where they are greater than dabbling, to allow them not to get an uhappy thought for going off-duty. This is often Masonry, as block production NEVER ends.
With the changes to vampire migrants, I'm now going to be forced to implement a two-tier system for migrants, where the first tier are my initial 7 and any 'known clean' migrants. (I am assuming that Toady is excluding Vampires from the initial 7. If this is not true, then we've just added another "whoops, you're screwed re-embark" reason to the list. The starting seven would have been the starting 5 or 4 when they if this were not the case...) The second tier are recently arrived and 'suspect' migrants, who will be burrowed into a rude soil dormitory and produce wood, food and booze for use by themselves. I'm still working out how I'm going to handle making the 'suspect' migrants something more than just a drain on migrant influx rates, as previous fortresses have been very much about securing migrant labor to fill in for bulk processing needs early to get the fort up and running smoothly, and there's a potential issue with making sure a large migrant wave finds the 'suspect dwarves' larder properly stocked before they run out.