Airtime Fairness
ATF feature addresses the issue where low-speed data transfers impact high-speed data transfers.
Airtime Fairness gives equal amounts of air time (instead of equal number of frames) to each client regardless of its theoretical data rate. This will ensure higher download speed to latest devices when slower devices are connected to the same AP. This is done to prevent slower devices from penalizing faster devices by monopolizing network traffic.
In effect this means that Airtime Fairness improves the speed for faster devices by making the slowest devices even slower. This may allow better Quality of Service for faster devices, and should be negligible for the slower devices in most cases.
Using band steering in combination of Airtime Fairness can further improve results.