There are towns and businesses on a map. Towns have consumption in normal (not zen) mode, businesses don't have consumption. Most towns and businesses have several resource requirements. If you complete one requirement but there are still more in that town/business the circle will be displayed as dark green. You can deliver more to overfill the requirement but you won't get any money for any resource delivered past 100% (circle becomes dark green at 90%, so for a short interval between 90% and 100% you will still get some cash). If you complete all requirements then such businesses disappear from the map, but such towns stay and they are displayed as orange circle. You can deliver more resources to those towns but you won't get any money.

Overfilling the green circle for towns is useful for difficult towns so you can focus on one resource requirement at a time. Overfill one resource, while first resource is counting down overfill the second resource, while first and second resources are counting down overfill the third resource, etc. Having more than 50% requirement completed reduces consumption of the resource so you want to get it as soon as possible and never let it go below 50% again, which is why you overfill one resource to be able to focus on others.

Green circle for businesses and orange circle for completed towns is just a resource dump. It can be useful only in rare cases where you need to find a place to dump some resources to get more experience for resource production industry. If industry output is full, then industry stops gaining exp, so you need to take resources from it and send them somewhere else. If there is nowhere else to send you just dump them into completed resource requirement for business or in already completed town.