Slavery, when it's use is efficient.
Slavery let as whip population for hummers.
On normal speed 1 population will produce 30 hummers. Each slavery whip cost 1 happiness.
Town size 1 needs 22 foods to grow to size 2.
So, roundly, 1 unit of food will produce 1.5 hummers.
With granary, it will be 3 hummers.
So, in best conditions, slavery converts 1 food to 3 hummers.
Towns need 30 foods to grow to size 5. With granary size 5 cities convert 1 food into 2 hummers.
What our other option to convert food to hummers?
Grassland hill mine convert 1 food into 3 hummers.
Plain hill mine convert 2 foods into 4 hummers.
So, if we ignoring happiness and health, Grassland mine is always better then slavery in any conditions. Plain hill mine become equal to slavery for city size 5.
Any town by default have 2 food, so if you happiness let you have size 2 town and it working 2 plain hill mines he is in optimum for hummer production. Any use of slavery will only decrease this town hummer production.
In addition, any act of using slavery decrease max size of town by one. For town at there max and having ability to work plain forest or irrigated plains cost of slavery come to 10 lost hummers.
I did try to create a table when slavery is better then normal production, but it is a bit to complicate and depends on available ties.
So, I just write basic conclusion:
When all food surpluses could be converted to hummers using grassland hill mines slavery is always a bad idea.
When all food surpluses can be converted to hummers using plain hill mines slavery is bad idea over town size 3.
When all food surpluses can be converted to hummers by plain forest slavery is a bad idea in town size > 5.
Slavery let as whip population for hummers.
On normal speed 1 population will produce 30 hummers. Each slavery whip cost 1 happiness.
Town size 1 needs 22 foods to grow to size 2.
So, roundly, 1 unit of food will produce 1.5 hummers.
With granary, it will be 3 hummers.
So, in best conditions, slavery converts 1 food to 3 hummers.
Towns need 30 foods to grow to size 5. With granary size 5 cities convert 1 food into 2 hummers.
What our other option to convert food to hummers?
Grassland hill mine convert 1 food into 3 hummers.
Plain hill mine convert 2 foods into 4 hummers.
So, if we ignoring happiness and health, Grassland mine is always better then slavery in any conditions. Plain hill mine become equal to slavery for city size 5.
Any town by default have 2 food, so if you happiness let you have size 2 town and it working 2 plain hill mines he is in optimum for hummer production. Any use of slavery will only decrease this town hummer production.
In addition, any act of using slavery decrease max size of town by one. For town at there max and having ability to work plain forest or irrigated plains cost of slavery come to 10 lost hummers.
I did try to create a table when slavery is better then normal production, but it is a bit to complicate and depends on available ties.
So, I just write basic conclusion:
When all food surpluses could be converted to hummers using grassland hill mines slavery is always a bad idea.
When all food surpluses can be converted to hummers using plain hill mines slavery is bad idea over town size 3.
When all food surpluses can be converted to hummers by plain forest slavery is a bad idea in town size > 5.