I do it here in California to protect myself, I’m not even sure if it is mandatory but I think it is. What I do know is that it is a complete waste of time. You don’t hear back from the Feds for a year if they respond at all.
It is illegal to use E-Verify in California
California employers, take note: On October 9, 2015, California Governor Jerry Brown signed into law AB 622, a bill that prohibits California employers from using the federal E-Verify system for current employees and applicants.
http://www.natlawreview.com/article/california-employers-face-new-restrictions-e-verify-use