Some subjects, like maths subjects and chem and even English subjects afaik where 1/2 is a foundation for 3/4 so it's kinda important to focus on them. some other subjects though, you can get away with not even doing the 1/2 and still do well on the 3/4 because the 1/2 is irrelevant, and for some subjects the 1/2 only equates to like 10% of the 3/4 content.
even, say, if you 'failed' 1/2 methods or something and if you work hard a good score is still achievable

(I did really shit in 1/2 - almost got an N but got a 30+ SS) ~ however, I do strongly recommend you do try hard in 1/2 cos a lot of the content is expanded on in 3/4 and I really wish I worked hard in 1/2 cos I had to play catch-up which sucked
but yeah, I do agree that you should try in your 1/2s anyway so you can 'get used to' how to cope with VCE content. I personally do wish I stressed harder in my 1/2s in year 10!
good luck
