If you ask for an ID, it needs to be as a "final touch" (if you will) too all the OTHER screening you've completed.
For instance, you've validated EVERYTHING about John SexyMan, and everything checks out, you feel wonderful about the situation, his refrences were legit, all that goodness...
The final piece is to see an ID that says in fact his is John SexyMan and he does live on Wanker Way, and his age is correct. It should just set in concrete everyting you already know.
Beyond that, ID's aren't good for much.