I totally disagree with the general consensus regarding dwarves skilled in soap and lye making. In any mature fortress I have the soap supply chain in continuous production. Every single one of my dwarves runs around happy from having had "a nice soapy bath lately" and no one ever dies of infection; plus I always have an overflowing food stockpile full of rendered tallow, so why not?
All newly arrived migrants skilled in a fiddly farming task like Milking or Threshing gets all farming tasks enabled except for Cooking and Brewing, which I prefer to be performed by experts, and Growing, because I track planters separately. Once I have enough "Farm Hands", I start drafting newcomers into the army. Put down that plow and pick up a sword, Urist McFarmboy!
Anyone who claims that a trained Strand Extractor is useless reveals themselves as a noob who has never actually dug out any candy. Because after you've waited however many months it takes for your Dabbling Strand Extractor to extract one freaking thread, you will never be unhappy to see a good Strand Extractor ever again.
Now, Potash Making, I have to agree that's pretty useless. I never have a fortress with working farms where I need even more food. Wax Working is also pretty useless; all you can make are crafts and wax crafts aren't any better than the crafts made from the stone you have lying around all over your fortress anyway. But if you have wax cakes left over from making honey/mead, it's not like there's anything else to be done with them in the current version.
Animal Caretakers, Trappers, and Animal and Fish Dissectors are the least useful as far as I'm concerned. Caretakers don't work at all, and Trapping then Dissecting vermin is a complicated process that in the end nets you only a trade good, if you're supremely lucky enough to trap anything extractable in the first place. These tend to be drafted on sight in my fortresses.