They tell my mother to spend a certain amount of money. No assets have been obtained, and beneficiaries have not changed.
Although I am not licensed in NY, I believe that this question can be handled with a very general answer, regardless of the state in which the trust exists:
Estate-planning laws may change rapidly and vastly, both at the state and federal levels. Also, both state and federal tax laws relating to estates and trusts may change significantly over very short periods of time. If left unaddressed, these changes may have a huge impact on the continued operation of the trust itself as well as the taxes to be paid from the trust on an annual and final (i.e., when the trust terminates) basis. So, even if the assets in the trust and the beneficiaries remain the same, the way the laws that applies to the operation and ultimate distributions from the trust may change.
By way of analogy, I always tell my clients to think of their estate planning the same way they would think of their investments. Would you hand a large portion--or all--of your assets to a financial advisor and tell them you'll review your financial situation with them in 20 years or so?
If only for peace of mind, I think most people want to know, on an ongoing basis, that nothing significant has changed within the state and federal estate-planning and tax laws that would adversly impact the planning they already have in place. Nevertheless, the estate-planning world is full of clients who do not follow their attorneys' advice and that also can lead to dire consequences.