Estate plans come in a wide range of quality. Some are very basic form documents that leave big holes open. Sometimes clients are given a will when a trust would have been better, or a trust when a will would have been better, because they did not get the proper advice regarding the benefits and disadvantages of each one.
I have had multiple clients ask me to review the plans created by other offices. These clients thought that they had a trust that would allow their estate to avoid probate, when in fact they actually just had a will. These clients had asked for a trust and were told they had a trust, only to find out after my review that they had a will with a testamentary trust that only goes into effect after their death and does not avoid probate.
I have had clients come to me with plans that do not protect the money their children inherit from full public disclosure of the assets/liabilities, from potential claims of a child's ex-spouse, or from their children's creditors.
In short, to answer the question, "Can I just do my own estate plan myself?", I often mention that some of my estate planning clients include lawyers who practice in other areas. These attorneys are aware of the intricacies that estate plans can contain. They ask me to do their plan because they believe that using an online provider or doing it themselves would leave too many holes in their estate plan.