Many people spend a lifetime acquiring assets and want to leave those to their heirs, beloved family members and friends -- not to the government. That requires shepherding the assets with great care so that the majority of the estate won't be lost to taxes. Doing so involves clearly understanding everything that can reduce the overall value of the estate. That way, when the government takes a big piece of the pie through taxes, there will still be some left to go to family members and friends of those whose labor created the estate in the first place.
When planning to leave assets to heirs, you want to consider what you have to leave to them, including money, real estate and other property. Maintaining accurate records of all of these is an important part of estate planning. Another important part of that process is calculating the debts that you have, so your heirs won't be caught by surprise.