I will bare my shame and say I still do not understand double clutching. I've read that with transmissions of old you would need to do it so you didn't turn the gearbox into a container full of assorted size metal chunks, and that modern semi tractors-trailer drivers use the technique due to the complexity of the gearings on their trucks. But why use the technique in today's manual transmission cars?
How is it any better/faster than just holding the clutch in:
push clutch down » shift to neutral » let clutch out » push clutch down » shift into gear » let clutch out
push clutch in » shift » let clutch out
Do you need a short shifter to experience a gain?
Is it something you'd only do in a purpose built rally/race car?
Maybe if I didn't have to press my clutch into the next timezone when shifting it'd make more sense.