It's hard to get someone's attention these days, but there is one area where people are actively looking for things that are new – and that's on their phone or pad.
People want to try new apps, they go out looking for new apps. They want to be entertained, find new ways to do things, to make their lives easier.
If you offer them an interesting app, that can be a far easier way of getting their attention than directly introducing your product or service. Through the app, you can introduce them to your real purpose.
You can also hold their attention through the buy cycle, when they are not in purchase mode, and build up awareness, respect and positive regard.
In this way, an app promotes ongoing interaction with a client and keeps working over and over for new clients; your return on your initial investment can go on for years.