A coolant overflow recovery bottle may have first been installed to keep coolant off the driveway, but it will help your cooling system perform better as well. When the coolant heats up it expands and some will exit the rad. This isn't necessarily due to the cooling system overheating, but because the operational temperature of the coolant is hot.
The system will perform better if there is no air in it. The way to keep air out is to use a recovery bottle.

I know someone is going to say they never had them back in the day, and it's correct to run with the coolant down a couple inches so it wont overflow when hot. That doesn't mean its not going to be more efficient with no air in the closed system.

It is silly not to have one, unless you have a 100 point correct show car, put one on somewhere. They can be hidden so it still looks stock or a shiny one can be added. I have a shiny one, not as good as a plastic one as you have to take the cap off to see the level. Plastic ones allow one to see the level without taking the cap off.

I have a buddy in Sugarland TX who works on a multi billion dollar LNG project. Heat exchangers is his specialty, tells me they have to be completely air free to transfer the most heat. Wont but a recovery bottle on his 69 because they didn't have them back then. Didn't have power brakes back in the day, or signal lights or heaters/air conditioning. May have noticed, this subject drives me nuts.