(I'm not up to date on the 2014 season, so a more avid fan might show me up) While the driver may be making adjustments to road-condition or in response to immediate problems detected in the car, the biggest reason he is going to have to fiddle with one of those knobs is strategy.

Shift the brake balance and you shift the tire wear, which might get you more time in certain corners in traffic, or might preserve a set of tires for an extra lap. The DRS is almost a no-brainer, but the KERS can require some finesse. Hit it into the turn, on the follow through, coming out of the straight? That depends on who you're up against, how his car performs compared to yours, and how you're looking on fuel & tires.

Also, FIA banned traction and launch control a few years ago, specifically because they were worried the computer was doing too much driving. Actually, they were worried that the top teams (Ferrari, Mercedes, etc) would be able to build a traction control so sophisticated that the lesser-funded teams would not be competitive.