This is a guideline only for the trustee in terms of who to pay a death benefit to.
The trustee isn’t obligated to follow your instruction. This may allow some flexibility however unintended distributions may occur.
One advantage is that it provides the trustee with guidelines as to how you wanted the benefit paid and to whom. They may still consider other circumstances and factors.
The trustee could use this discretion inappropriately.
Unintended distributions that are not wanted by the deceased member may occur.