To varying degrees.
Maths - the oft quoted '30% Prelim can be tested.' 100% of Prelim is tested - there's no way you can do Year 12 Maths without knowing the entirety of the Prelim course.
In my own experience:
Economics - its good to revise the Year 11 content - especially supply/demand curves and other diagrams, market failures, etc. Not essential, but it will make things less complex in Year 12
Ancient - Forget Prelim
Studies of Religion - revise the basic sources of ethics for your religious traditions
Business Studies - largely forget prelim. Obviously, remember the business functions, marketing mix, pricing strategies, etc.
English - Forget Prelim.