What does 'not well' actually mean? In terms of marks, ranking or actually failing the entire unit altogether?
If you are talking about receiving an N overall for a unit, this could potentially have ramifications. A quote from the VCAA Frequently Asked Questions:
However, VTAC advises that for the calculation of the ATAR, students must satisfactorily complete both Unit 3 and Unit 4 of an English sequence.
So essentially to be awarded the VCE, you have to complete 16 units overall (which basically means four subjects of Unit 1-4.. or an equivalent,
at least). If you fail a unit completely, you don't have much wiggle room.
In terms of ranks/marks - all that matters is your
rank. Is it possible to recover from poor performance in Unit 3? Of course it is. Is it an ideal position to be in? Not really. The exams still remain the most important aspect of a subject.