Originally Posted by
Setanta
Double clutching is entirely unnecessary on the streets. That's why you have synchros. Push the clutch in, pop it in gear and release the clutch is all you have to do.
On the track, heel and toe IS part of effective gear-changing and part of the double-clutch process but TBH, I only double clutch on the track on corners that involve huge rev-matches.
I'd suggest watching the super-taxi (falcodore) series of motorsport, they always do footwell footage of double-clutching (arguably more interesting than the race itself) and you can even see them shift without using the clutch on occasion (entirely doable but not recommended in your daily driver if you want to preserve your gearbox - borrow a friend's car to practice :D ).