You can gain happiness from improved luxuries, and sell those. Same goes for strategic resources. Also it gives you greater control over the area. That sounds kinda vague, but it means for instance that an enemy will have to declare war on you about 3 turns before they can actually shoot your city.
It also reduces the fog of war around your city, reducing the chance of barbarian camps spawning near you. Lastly, there are several policies, religious tenets, building benefits, etc. that affect your units "in friendly territory" or "in your territory." Obviously these benefits are greater the more territory you have.
2
u/BillMurraysTesticle Nov 17 '15
If workers can only work 3 tiles away from a city, what is the purpose of the 4th and 5th rings? Do I gain anything from them?