The most beneficial reason why your business needs an APP is  a WIN WIN situation  for your business and your client. 

With your App installed on their phone, your clients have your business details at their fingertips and don't have to search for it.

And you have the opportunity to send out Push Notifications whenever you need to send out important information about your business.

 Be it the latest special, a Discount of some kind or some Covid related issues where you  can let your client know whether you operate as normal or are closed because of another Lock down to stay in touch with  your customers / clients.  Because guess what? With your APP  you are in your customers phone at their fingertips every time.