Just like knowing how to drive stick is useful in case you jump into someone else's manual tranny car, knowing how to double clutch is good if you find yourself in a car with no synchros. The Formula Dodge cars they use in the Skip Barber racing school have no synchros, so you're forced to learn double-clutching. I try to practice it as much as possible. Now I need to learn to heel-toe while double-clutching the downshift. It's like musical chairs for your feet!