This is just a general question. On the farm we take (in my opinion) very good care of our equipment, but coolant changes are just one thing we never do. Our fleet is 20-40 years old (except for the tractor in my sig), and we never do coolant changes unless the motor has been taken apart for some other reason, and we don't seem to have many cooling system problems. I talked to Dad and Papaw about it, and they just don't see the need for it. Does it prolong radiator life? In my life we've replaced the radiators on maybe a quarter of our trucks and only two tractors. I flushed my car a few years ago just for the heck of it.
(we've got 23 licensed vehicles and 14 tractors)

Its overheating and antifreezing capabilities weaken to the best of my knowledge. So in extreme conditions, your old antifreeze might not work. With dex, of course, its different...it just turns to sludgy acid

Corrosion protection additives in coolant become depleted after approximately 5 years. If the system is tight and has no leaks allowing air to enter, maybe this is not a huge problem. But, I have worked on cars whose cooling systems were in horrible shape because coolant was never changed. Maybe they had leaks that allowed oxygen in to corrode the components. Coolant changes became a whole lot more important when GM started filling cars with Dex - that'* for sure.