Should I downshift when braking my car?

Tiptronic is a type of discrete automatic transmission developed by Porsche and used in its vehicles and those of its licensees. A Tiptronic transmission can operate just as the common type of automatic transmission, but it also allows the driver to override the automatic mode by moving the shift lever into a second (Tiptronic) shift gate equipped with two spring-loaded positions: "upshift" and "downshift". Once in this gate, the driver takes over most of the shifting decisions ordinarily performed by the transmission's computer, permitting, for example, the delaying of an upshift for increased acceleration or explicitly commanding a downshift to increase the braking effect of the engine. On some cars, the upshift and downshift operations can also be commanded by pushbuttons or rocker switches installed on the steering wheel with an optional display in the instrument panel indicating the current gear selection.