Your workers should not be able to repair enemy improvements

[qqqbbb]

It makes capturing cities trivial. You bring a couple of workers with your siege army. When your units get low on health they pillage improvements near city they siege and your workers repair those improvements.

[ydhuang28]

Don't see why that can't be a viable strategy. If you are willing to take the risk of losing several workers, then you should be rewarded. Also, should depend on vanilla mechanics.

[qqqbbb]

Also it can used as a source of free gold.