Mobile apps are extension of your website but are becoming more relevant now due to users availability over smart phone more than any other device. Apps are installed on users device so they become a part of their communication eco-system.
Mobile apps not only give them device friendliness over mobile but also provide more engaging and personalized user experience. It gives us much better understanding of specific user behaviour.
Mobile apps are also governed by different technologies, operating systems and device needs. The idea is to provide a seamless experience whether user is on website or tablet or mobile and keeping his convenience over device in mind.