I know of a few reasons NOT to use antifreeze all year.
One reason is antifreeze will run hotter than water since it does not transfer heat as well a plain water.
Another reason is in hot or mild weather the small amount of protective additives in A/F will quickly become ineffective and will cause many issues in the cooling system.
In a short time the coolant solution will go acidic and cause silicate dropout, especially in the radiator which is evident by the hard, white deposits around the tubes.
We have seen this in very low mileage cars which had radiators 50% clogged that seldom, or never, had the A/F changed.
An obvious reason NOT to run A/F if it is not freezing weather is the the ethylene glycol will immediately damage soft bearing surfaces if it comes into contact with it.
Commercial A/F has a minimal additive package as this is the second most expensive item, the marketing and advertising is the most expensive.
For years we have recommended that RMI-25 be used with A/F to help protect the cooling system.
Since we are very aware of the importance of a good cooling system in our climate to protect our expensive engines, we highly recommend flushing A/F every spring, and use RMI-25 the rest of the year.
If you really believe the ad guy's hype of A/F lasting 5 years and 150K miles, let me know how that works out for you?
Your cooling system with iron, alum, copper all in solution is the basis of a wet cell battery that will attack/corrode and remove metal, especially the aluminum.
If you insist on your method, it would be smart to add RMI-25 at least twice a year. This will cost you about $5 a treatment to protect parts that are much more expensive!
