you don't HAVE to. but, you'll probably do better if you do one- just to get ur ideas together, devise diabolical sentences, witty conclusions and whatnot.
but if u're one of those alien life forms who can still get 15/15 without doing that, then.. good on ya, kiddo!!
if ur not going to do a practise essay, then at least get ur points ordered in ur head & think about the examples etc..
depends who u are, i guess.
but i reckon that if anyone did a practise essay, rather than not doing one- then their mark would almost definitely be better....
practise makes perfect!!