Double clutching was once a required technique. It was used to sync the engine and transmission speed. In older cars without double clutching you were unable to shift (you even had to double clutch to up shift). However, in new transmissions synchromesh gears do most of that work. While the synchromesh gears reduce the need for double clutching, they don’t handle the large changes in speed that go with down shifts very well. Double clutching makes the downshifts smoother and saves wear on the transmission by reducing the amount of work done by the synchromesh units. So go out and practice a double clutch down shift (in a safe place), it’ll save you precious money on your transmission. Practicati asa ceva?