They're not 'important', but they never hurt (well admittedly, some can). If you have the motivation, determination, support from friends / parents / teachers, access to resources, intelligent and experienced teachers than it isn't required.
It really depends on the individual. Having a tutor provides the supervision when studying, the access to another resource who can provide advice and feedback when needed, and a motivator to keep you going throughout the year. Some students need this 'supervised learning' due to the lack of determination, but if you're aiming for a high ATAR anyway, you should have the drive and will power that is needed.
Good luck this year though.