Using fuel injector cleaner that you add to your fuel tank does help with keeping your fuel injectors clean as well as clean your throttle body out on the inside.
I use STP fuel injector cleaner and it does improve my gas mileage by around 20 miles per tank so I get 20 more miles out of a tank of gasoline when using the STP fuel injector cleaner in my gas tank after filling up.
I always keep a bottle or two of STP fuel injector cleaner with me in my truck and car and after every second fill up of gasoline I add a bottle of the STP fuel injector cleaner to the gas tank.
You don't want to add fuel injector cleaner or other fuel additives to every gas tank fill up because it can cause more harm than good.
But adding fuel injector cleaner to your gasoline tank after every second gas tank fill up can help keep your vehicles engine running smooth and prevent your fuel injectors from clogging up.
You should notice a slight increase in your fuel mileage as well.