I never automate my workers.
Automated workers do crazy things, like:
One worker tears down a cottage to build a farm, while simultaniously on the neighbouring tile another worker tears down a farm to build a cottage.
When not at work, they hide out in cities. If an improvement then is needed in another city some distance away, the sleeping workers do not pick up on that and continue
Or, if they do pick up on a tile in need of work, all the workers rush to the same tile whilst other tiles in need of work will not be touched.
In addition, all automated workers seem to spend a lot of time building forts all over the place.
And they roughlessly chop down every forest, leaving no opportunity to build lumbermills or forest reserves.
And if you mark for "Automated workers leave forests" and "Automated workers leave old imrovements" they will not improve any jungle or forest tile until replaceble parts, then they build lumbermills everywhere (in forests) and when forest reserves becomes available, every jungle square becomes a forest reserve. They simply don't care about the terrain under the forest/jungle.
As for leaving old improvements, if they have made a mine on a hill, that mine will never become a windmill, and if a late resource (like coal) appears where there is a windmill, they'll never build a mine.
They know that something is needed, though, so they pile up on the spot and "hang out", waiting for something to happen.
And all of them just stay there, idle on the spot, whilst other tiles do not get worked due to lack of available workers!
And then the cities will start begging you to build more workers, since you obviously havent got enough of active workers.
And if you put them on automation for building trade network, they do start off by building a road from one spot to another, but when passing a resource, they get "sidetracked", leave the roadbuilding and start improving the resource. And then they spot another resource and .... ..... ..... What happened to the roadbuilding?
Automated workers =