In Harry Potter, we all know there are long spells and short spells. Pronouncing long spells takes up more time and the wand movement is often more difficult, so how can they be useful in a duel? Short spells like "Stupefy" are easy, fast and rather powerful, "Protego" is too. What's the advantage of knowing and using long spells against a wizard who uses short spells?
Say we have "Petrificus Totalus" which can be helpful, but is long, it is pretty easy to counter-spell "Protego" and then cast "Stupefy", so will a wizard using short spells always win a fight?