This is a question that I use to get when we first started in 2009 when everyone was still using paper maps and programs. Since that time, however, I do not get this question often enough.
Just producing a mobile app does not mean it will be successful. Sadly, some organizers buy an app just to have one or they got it for free (ok, don’t get me started on a free app – you’ve heard the old saying “you get what you paid for”).
More information: http://www.eventapps.com.au/why-have-a-mobile-event-app/