My owner's manual says to never use less than 87 on my motor. Pick a higher grade until the octane is 87 or higher. I've been in winter high elevation locations where they had 85 octane and had to get premium grade just to get the Octane I wanted.
Top tier claims that it improves fuel economy, prevents carbon deposits from building up and cleans deposits after a few tanks of gasoline. My interpretation of that is the fuel is burning cleaner. Carbon build-up in the combustion chamber is prevented and therefore cleaner burn over time.
First and foremost it is a design issue. But the only one related to the user is the oil.
Depending how much gas you use, the amount you save at Costco gas stations alone could cover the cost of membership, check the prices, drive through there when they are not busy (rarely) or closed.
