A trust where the trustee controls the flow of money on behalf of the beneficiary is known as a "spendthrift trust" and is quite common form of testamentary trust in the US. Typically, it's used in cases where:
- The beneficiary is unable to control their own spending (hence the name "spendthrift"), and the grantor wants to ensure they have long-term support for essentials.
- The beneficiary is a minor or has developmental disabilities.
- The beneficiary has other special needs, and is eligible for needs-based government assistance. Because the money in the spendthrift trust isn't theirs, it doesn't hurt their eligibility as a direct gift would.
- The grantor wants to use the assets in the trust as an incentive to get the beneficiary to do something, like finish college.
- The grantor wants to protect the assets in the trust from being "attached" if the beneficiary is sued for some other reason.
In general, the mere existence of a spendthrift trust wouldn't be considered abusive or against public policy. It is the right of the deceased to decide whether to attach conditions to the distribution of their estate.
Courts are very reluctant to modify a trust unless a) its terms are ambiguous in some way, or b) the trustee's behavior is clearly not in line with the terms. In theory, if there was clear evidence that the intent of the trust was abusive (such as a discussion between the grantors to that effect), the trust could be revoked as a matter of public policy. But, the threshold of such proof would be difficult to meet.