You can provide for a loved one with special needs without disturbing valuable government benefits.
You could also supplement the income of a child who wants to be a teacher or do other low-paying -- but very important -- community service work.
Most people like to leave their children or grandchildren with enough so they can do anything they want, but not so much that they do nothing.
With a trust, you can do this. No other estate plan gives you this much flexibility and control.