Do you want more meat on your animals? Tired of micro-managing your careful eugenics programs for your Dwarves's wholesome food source?
If not, it's still an excuse to drown things.
That's reason enough.
One day I happened to come across the idea of using the undead to preserve corpses, and by extension, later preserving bacon for a Dwarf vault. On the occasion where the notion that becoming undead instantly makes something more muscular, the two facts clicked in my mind.
Zombie bacon farms.
If you haven't caught the gist of the situation here - there's a way to garner more meat from your slaughter.
What you need:
1. A source of undead evil goodness. A necromancer or evil biome with spooooky interactions will do just fine.
2. A source of meat.
First, start building a drowning chamber.
Here the necromancer has been brought to the construction sight, to build fear of her upcoming demise. Leave her guessing as to what the Dwarves have in store.
It need not be anything fancy - it could just be a hole in the floor for all it needs to be. As long as you drown things in it, it's good.
Next, secure your source of necromancy.
The windows are so she can see the water rising. The bars are placed in a way that the water depressurizes when it enters the smaller sub chamber. This makes the water level inside rise slower.
Add your livestock. For purpose of demonstration : Three pigs and one dog.
Assemble the fortress for the demonstration.
It's funnier when you bring the family.
PULL DA LEVER
Not exactly weak animals, but the weak had already been slaughtered. They'll still serve for the purposes of the demonstration.
In retrospect I probably should've chained up the animals.
Drop by drop...
Dammit they are smart. Really should've chained them up.
At this point they started drowning, and I released a lot of the water. Apparently necromancers cannot animate corpses whilst drowning. Shame.
Size bonus and muscle bonus. Moar bacon for all.
And I may have forgotten about the necromancer still being alive for just a second.
Notes: The drowning just ensures the corpses stay fresh and uninjured, ensuring maximum yield. I originally tried it with a regular ol' evil biome, and I'd say it works better than with a necromancer, mainly because whilst the animals are drowning, the undead can still hurt them and potentially sever limbs, lowering bacon yields.
Also if you want to drown the necromancer for funsies, make the chamber at least 3x3. 2x1 is too small apparently, it was a very close call.