There is some talk from time to time to formalize criteria but in general any competent arbiter can ask to be granted this title. In a recent discussion, it was proposed that perhaps we should require two arbiters to vouch for candidates.
The main benefit is that they can be arbiters at a FIDE rated event. It is the first rung on the ladder of FIDE arbiter titles. I believe that it may also be required as a precondition for attending an arbiter seminar.
We want more national arbiters as they are necessary for the infrastructure to hold FIDE rated events.