It depends on your diet and your health history. It's easy to say, we have access to good quality fresh food here so you don't need it. And to an extent that is true - if the person eats healthily and has done so for a very long time. However if you have for example, gut damage then your ability to absorb nutrients from fresh food is going to be lessened. The multivit thing, well, if you are of average health and energy then the added minerals and vitamins will really be supporting your health, moreso than baby. Baby takes everything from us (don't we know it). Like that old saying, a tooth for a child. Classic case of calcium deficiencies maybe?
There are certain things that are deficient in most Australian diets. Iodine for one, which is crucial for brain development throughout breastfeeding as well. If you eat fish 2-3 times per week you'll have it covered but it's not present in much else as our soils are, overall, lacking. And not many aussies eat fish 2-3 times every week.
If you feel well and have no health problems then you probably don't need vitamin or mineral supplementation. You can also target areas with certain foods rather than a pill (kelp or fish for iodine for example). Food is always best really. I have taken multivits & fish oil religiously in this pregnancy as I've suffered a miscarriage, and have long term identified deficiencies. It's very personal.