Is someone able to give me some general pros and cons of studying undergrad medicine straight out of Year 12?
As a preface positions for undergrad medicine are quite limited and if you do find yourself in a position where you have an offer for undergrad medicine, personally I'd think it'd be a tough decision to forego that offer for a chance to apply for a postgrad position (but of course there are other very legitimate reasons to decline an offer including not wanting to study med at all/Chancellors Program at Melbourne).
Other pros for undergrad/high school direct entry:
Shorter (but a few years imo isn't a real waste of time - you're still making friends, developing life skills etc even if it does feel like that from a high school perspective)
Strictly speaking - an extra year (or two) studying medicine in an undergrad course (4 year postgrad are strictly speaking more compressed/rushed but they are still designed to teach you everything about being a competent doctor - and this applies less if you're going to do biomed degree beforehand)
Cons:
Less ability to explore other academic interests (though there are some options like Diploma of Liberal Arts/Languages at Monash, it's substantially less than completing a degree in something completely unrelated at uni)
Not knowing if med is really for you (this is an important one - the journey to be a doctor is a lifelong one and having more time to decide can be valuable)
Maturity (jury's out on this one - personally think it's very possible to be a competent and mature junior doctor at 23 and the consensus is that graduates from both courses function at comparable levels)
Stress - you do hit the ground running in the preclinical years of med so if you're feeling Year 12 was stressful it can sometimes feel like more of the same if not tougher
Obviously a biased view of things - but I personally feel like taking time to think about what you really want from a career in medicine, whilst recognising that a decision you make now isn't going to be a permanent one that will be forever unchangeable can be helpful.