When a right of appeal is removed, what is removed is a valuable and necessary constraint on those who exercise original jurisdiction. That is true not merely of immigration officers but of anybody. The immigration officer who knows that his decision may be subject to appeal is likely to be a good deal more circumspect, careful and even handed that the officer who knows that his power of decision is absolute. That is simply, I fear, a matter of human nature, quite apart from anything else.

Source