Yes they do something, yes they work. I have been to the wind tunnel and have numbers to back it up.
From Race Louvers: "
Note - For maximum efficiency we recommend the inner fender liners be removed. If the inner fender liners are to be retained we recommend cutting a hole in them near the louver and covering the hole with a screen, this will make the louvers functional while still providing protection from debris.
Race Louvers is proud to offer our new FL fender louvers for the rear lower area of a front fender. They are design to extract air from within the front fender area increasing front downforce, improving splitter functionality and improves cooling by pulling air from the bottom side of the radiator. The lower fender pressure also aids in front brake rotor cooling as brake duct airflow is increased."
https://racelouvers.com/brz-fr-s-86-...l-fender-trim/
https://racelouvers.com/brz-fr-s-86-...f-fender-trim/