This is a very good question I found here. Not all apps are important to a business but some apps must be installed in your smartphone to run a good business. Suppose you run many blogs of different niches and you need instant reporting of visitors and AdSense impressions. Then you must have Google analytics and Adsense app installed on your phone. This is just an example.
With these apps, you also require some security apps for your smartphone. This is because in this time of internet lots of hackers are active around the globe and these apps can save your confidential data.