The Wall Street Journal had an interesting story regarding the decanting of a trust when it is appropriate. When a farmer sets up an irrevocable trust and funds it, it is normally extremely difficult to change the structure of the trust, even by the farmer. This usually involves a costly trip to the courts to get terms changed.
Decanting allows a trustee to change certain terms of a trust by "pouring" the assets from an old trust into a new trust. So far, 21 states have adopted decanting laws, with Wyoming being the latest.
The trustee can't change beneficiaries' vested interests in the trust, but for example, the trustee can change the trust to another state with more favorable terms or push back the age when a beneficiary can receives a payout.
Decanting usually costs about $2,500 to $10,000 versus multiple $10,000 for a trip to the court to get a trust changed. Another provision of decanting in certain states is the ability to set up multiple trustees for each function such as handling investments, handling the payouts to beneficiaries and perhaps one for handling the trust paperwork.
With more and more irrevocable trusts being set up by farmers, it may make sense to use the decanting process if your goals for the trust have changed.