lyounamu said:
Are you confident with all your 10 units? If not, better stick to 11 units to have one unit to fall back on.
Personally, I don't see the reason to do 11 units or 12 units if you are extremely adept at everything you do. So make a careful decision as it only comes once.
I agree to an extent. I think that it is good to have one or two fall back units, the only thing which I don't agree with in your post is that what is the point on having the eleventh fall back unit if it will probably be your worst and won't count? By the sounds of it, this person is having some troubles with Extension Maths, and it will probably be their worst unit, so if that is the case, why keep it if it will detract from your focus on the other ten?
Of course, this person may do well in the HSC Extension test, and bomb out in another, so the unit maybe helpful, but from what I gather, the odds of that happening would be slim.
I do agree with the last part of your post, if you are doing well in 10 of your units, you may as well concentrate on those ten, rather than dragging one or two which you won't need.