The short answer is: quite a few, but not a lot! It really depends on your circumstances. Let’s look at it from different types of circumstances and which Will fits best.
1. The single young(ish) person/couple with no children. A Simple Will may suffice. You give your estate to your parents. Failing that, to your brother and sister. Nothing controversial in the family to warrant much more.
2. You have children but they are not adults yet. You have some assets, but decent Superannuation and/or Insurances. People sometimes forget that these Supers or Insurance can form a large part of your estate (say another $1 million). So a simple will is sufficient. But are you happy with the children having, say, $500,000 each at 18 years of age? And bear in mind these monies will be in their bank account and vulnerable to the world, e.g., divorces, creditors/bankruptcy, children that are easily led. If this is a concern, then a Testamentary Trust that gives control of the funds by someone you trust might be more comforting, as the inheritance is then protected from divorces, creditors/bankruptcy or people influencing the children— but they still get to enjoy their inheritance, and this can include grandchildren.
3. Marriages where there are children from other relationships. Say you wish to make sure that your estate goes to your children and the other person’s estate goes to that person’s children. What happens if one party passes away 10 years after the other? A Mutual Will or similar, if drafted appropriately, can ensure that, say, after the final parent passes, their estate is divided to both children from both families.
4. Then there is the case of parents with adolescent/young adult children. A Right to Reside may be preferred, i.e., if something happened to both parents, and children may be, say, 12-20 years of age or a little older, then if they wish, they can stay in the family home (with guardians) until, say, the youngest child turns 25 years. Then after that, the family home is sold and divided amongst the children equally (or however you wish to deal with that asset). This can allow adult children to save (by not having to pay rent or otherwise use their inheritance for such things), or allow the children to feel more secure in the family home after traumatic events, as opposed to the family home being sold, forcing them to move on to somewhere else.
These different types of wills should be part of the discussion with your lawyer and should not be significantly more in costs. They give you peace of mind and save your estate potentially tens of thousands in claims, challenges, protection. When one compares the costs to that of claims, it is a drop in the ocean.