Not legal advice. A summary of what I have found, is all:
In theory, it means you no longer have a conviction. It's meant to help people clear their past, start afresh. If your application asks if you've been arrested or convicted of a crime, in theory- you can say 'no', unless the question specifically ask about convictions that might have been expunged). However- government agencies (as in BON) still have your conviction record, forever, and more and more data banks buy arrest information and sell, it, making it available online. It's just all over the Internet. So you are convicted, get that expunged, apply for a job, tell them 'no' convictions...then they find your arrest on an online data bank. Kiss the job goodbye, because they found out what was not supposed to be able to be found out, so you 'lied'. Also, as far as the BON is concerned, you have to report any black mark against form your enitire life, it's just the way things have become. Nothing ever goes away.
Today, finally, after two years of questioning whether to attempt to clear my own record, I finally found a lawyer that sums this up real simple: "Expungement is a waste of money and time. As soon as you are arrested, those government agencies sell your arrest information to mass marketing firms, that spread it around the globe. Even if expunged, that cat has been let out of the bag. And those sites do not correct your arrest information, even if you are then found innocent. I don't recommend it to any of my clients, regardless of the crimes they have been charged with or convicted of".
She went on to say that if you find a web site that still lists your conviction after it was 'expunged', you can petition them to remove it by conditions in the Fair Credit Reporting Act. But it will also be a waste of money and time, because there are so many of these data mining sites.