Boosts can enhance your Driver and Component stats, with the exception of the Qualifying stat. This is because you have the option to allocate Boosts to your Drivers following the qualifying session.
The possible Boost effects are the following:
Overtaking
Defending
Race Start
Tyre Management
Speed
Cornering
Power Unit
Pit Stop Time

A boost is consumed on race start and each time a driver pits during the race.