Even if you are found not guilty, a charge against you was dismissed or dropped, it will still show up on your record.  A background search of you will show that you were arrested.  Perhaps you are applying for a job with a security clearance or job that is sensitive in nature, a background check showing you were arrested for anything at all may be a huge factor for a prospective employer and their hiring decision.  

Sometimes people make false accusations.  Because of these false accusations, you could find yourself being arrested for a heinous crime.  Later on, the charge against you might be dropped by a prosecutor or you are found not guilty by a judge or jury.  Unfortunately, even though you were found not guilty, the record of your arrest will remain on your record for life.  You can have these charges expunged.  In doing so, all records of your arrest are erased so a background check should yield nothing in regard to the incident.  

PLEASE NOTE:  Expungements are only available for persons whose charges were dropped by the Commonwealth Attorney, charges that were dismissed and charges where a person was found not guilty.  If you were given a first offender resolution to your charge and even if you successfully completed the terms of your first offender conditions and the charge against you was dismissed, the arrest cannot be expunged.  It will show on your record that you were arrested but the charge was dismissed.  Furthermore, if you were convicted of anything, even if it has been decades since you were convicted, those convictions cannot be expunged.