To perform an emergency stop (or a full stop in general, I suppose). The picture shows the brake pedal and the clutch pedal being pressed, not the gas and the brakes; you can see the accelerator to the right.

If you don’t free the clutch while coming to a stop, you’ll probably damage your car. This is especially important in scenarios where you can’t reliably shift down fast enough to keep up with the car’s deceleration, for example when doing an emergency stop.

In normal braking scenarios you probably want to keep the clutch engaged until you hit a low RPM (where the engine running without acceleration is trying to accelerate the car, rather than braking on engine power alone). That way, if you need to accelerate to evade, you can do so quickly without connecting the clutch first.