Communist forts let you easily switch from one thing to another.
Want to build a wall really fast? Done!
Want to burn 2,000 logs into charcoal? Done!
Want to cook thousands of roasts? Done!
This is a very good point, but a) it's rare that I want only one thing done, and b) when I do, the numerous haulers I keep on hand make the perfect surge force, getting a big job done quickly while not distracting the specialists from their gainful work. A few clicks in Dwarf Therapist is enough to mobilize the horde.
Some additional points:
- Many jobs require multiple steps. Assigning a horde of dwarves to do a multiple-step job is tricky at best. It's quite all right to tell the horde to use up an existing pile of materials (like blocks for a wall), but having them first plant, then harvest, then cook gets you an awful lot of dwarf-hours wasted, quite apart from the lack of effectiveness per dwarf and low final product quality (why feed my dwarves, or try to sell, crappy food, when a skilled cook can do so much better?)
- Having the horde do jobs that affect strange moods ruins any plans you had for encouraging desirable moods (like armorsmithing) instead of just getting legendary engraver #8.
Also everyone gets all sorts of attribute bonuses, which means every dwarf is pretty much maxed out as far as attributes go.
(ignore the following; Hyndis has noted that this is a bug, now fixed) Unfortunately, this no longer applies in recent versions of Dwarf Fortress. Most skills (possibly all skills other than military ones) don't affect attributes. I'm not sure of the particulars, I just know that you can't just train dwarves in civilian skills and expect them to get stronger, tougher, or more dexterous.