hmm...from previous comments
i agree with Morgues, if u do 12, u waste ur time on something that doesnt count
in my situation, im fukking up physics badly, and it looks like ill do worse in that that than my 79 in SDD last yr, but 1 unit of phys will have to count cos i do 11 units...if i could drop phys and concentrate on my other subjects, in which im doing pretty good, i wouldnt have to waste valuable study time for physics, which wouldnt count anyway (but half does)
BUT in saying that, most ppl do 12 or over simply cos they want/need the knowledge for university