SeanOC

  * You make attendees more mindful of their actions.  Often people who commit sexual harassment don't really realized the full extent and consequences for what they are doing.  By stating that this type of behavior is unacceptable, upfront, at least some people will be a bit more likely to think before they act.
  * Should something happen, the path to action is clear.  Running a conference is a bit of a crazy job.  You're keeping track of a hundred things at once and dealing with a dozen people's problems.  This is not the best state to be in when you need to decide how to handle a delicate situation.  By stating upfront how this type of behavior will be handled, it takes a load off of the organizers' shoulders on the day off.
  * A strong signal is communicated to people who are concerned and possibly afraid to attend an event.  People go through all kinds of horrible things in life.  Often those experiences leave people (understandably) cautious about situations that might lead to similar experiences.  By having an explicit policy, people with fears and concerns are given a strong signal that the event in question will be a place where they are safe and welcome.