Boost is really about track knowledge. While I mostly agree that I'd rather the drivers manage it, there's a very high chance I'd never actually turn on the option since I want my strategy to work a particular way. Unless they open-source some of their code, I have no idea if the driver thinks the same way I do.
It would also be nice to be able to enter a new setting to choose how the pilot should use the KERS, similar to the push level.
KERS always used by the pilot and also by the manager during the live races.
As it is now the KERS looks like a cheat : /
There used to be an option in the live viewer allowing managers to select between automatic (managed by the AI) or manual KERS usage. It's one of the few options/features removed from the game that makes players ask "why?"
Still, KERS management plays a huge role in race tactics and on-track battles in this game, especially when you reach the Elite tier in a competitive league. Live managing KERS well allows you to be more competitive, and is a skill that you'll only be able to hone if you live manage. It is one of the essential skills that decides who's the best among the best. Often in competitive leagues, any close finishing gaps you see in the results are in fact determined significantly by KERS management and on-track battles that the final results do not necessarily do well to reflect. For a reference, Gustavo Heiden from US Grand Prix has posted some videos of the KERS battles that take place in the Elite tier of his league.