Lets go through each point:
Tutoring can be used as 'forced motivation', forcing you to study even when you've lost focus at school:
If you are so dumb-shit retarded, that you can't stop playing farm-fucking-ville or being on BOS for 2 hours a night (in an otherwise...8 hour night?), then you don't deserve to get a decent ATAR. Motivate yourself...Think, if each millimetre represented a year, and you live, lets say 8 cms (80 years), year 12 is one millimetre on that line...a millimetre which could influence the rest of the line...If that can't get you motivated, drop school, and start packing shopping bags.
Tutoring can be used to catch up on work that you've missed out on school (for whatever reason).
This is perhaps your best point. However, i fail to see why a dedicated, or even "smart" student couldn't ask the teacher, go on BOS, search the internet or even, dare I saw, look in their textbook, for help on the missed work, thereby negating any need for tutoring.
Tutoring can be used if you feel your school is too slow and you want to get ahead, but you're not sure how to study yourself:
Wow...How lame. One point at a time but.
If, as you say, smart people go to tutoring, what makes smart people smart....In general, their ability to grasp concepts. If this is the case, and if they have the motivation (see point 1), anyone can grab a textbook, sit down, and learn ahead. Maths/science/english isn't exactly hard to self teach....I mean, if someone had to actually develop the concepts and prove identities, then I see no reaosn why anyone could not just learn from an already provided textbook, even asking their teacher for help.
Next...You will be studying for another...3-6 years after school, and have already been "studying" for at least 3 years. If you do not know by now, you are in trouble. Year 10 is the perfect time to try out various techniques (which are easily avaliable from websites) and see what works best. People should not rely on someone elses methods, everyone is different.
And last but not least, tutoring can be used if your teachers are shit:
This is another lame call...Some teachers are generally poor, but EVERY school has at least one good teacher you can talk to. Additionally, if you listen in class, ask questions and actually, hmm, Idk...read and review the textbook before and after the class, you might find it a lot more beneficial.
Now, I know this all sounds tough, but it's tough because it is reality.