One of the best reasons to do estate planning is just to stave off family disputes before they begin. Without a plan, heirs will often argue over all manner of things.
In some cases, they disagree on who should get specific assets. Two children may want the same mementos from their parents' home, for instance, and they have no guidance. They both feel like their parents would have wanted them to have it, but how do they solve that with no proof?
In other cases, they may disagree on what roles to take. The estate plan can name an executor for that estate, and that person is in charge of things like gathering assets, paying taxes, paying debts and splitting everything up. One person may say that they'll do it, but others could disagree, perhaps based on a history of poor financial choices. Just picking someone for this job can grow contentious, and the job has not even begun yet.
Perhaps the most contentious cases as those where a person claims they should get more than someone else. Maybe one sibling stayed near home and took care of his or her elderly parents. The other sibling went off to live a life abroad. When the parents die, that sibling who stayed home may want extra money to compensate them and may feel resentful of the sibling who was off doing their own thing. But do they really deserve an unequal split?
These are just a few of the ways disputes can arise, but they make it very clear why people need to consider their estate planning options and take the proper steps to make things clearer for their heirs.