Ducting/exhaust tuning for better aero.
The F1 duct does not involve any pressurized or blown-air (ironically also called 'blown wing') just a pressure differential fed through slot gaps of the rear wing, cause stall conditions & lessen downforce of wings. Benefits on the top end speeds.
There are also the Red Bull 'blown floor' or double diffusers, to create more downforce. The rear-pointed exhaust gases help redirect, control & accelerate underbody flow for more effective venturi bottom.
Exhaust Driven Diffuser
And this year's aero trick shows up in Renault's exhaust system, blowing exhaust forward?!! Supposedly to accelerate & buildup high pressure regions @ the back.
Renault R31 Front Exit Exhausts (FEE) – Explained « Scarbsf1's Blog