What does the mill do?

I purchased the mill on level 15 but I can't see that it really produces anything! What am I missing--please?

The Mill takes what used to be 1 food and increases it to 3 food. Whenever a worker harvests food, he immediately takes it to the Mill.

It increase garden grown food 3 for 1, not food picked up off the road. Moreover, if an enemy is between the garden and the mill, the worker will just take the 1 food back to base. The saw mill does the same for tree grown wood. The forge does the same for mined gold.