Apps are brilliant tools for engaging your customers, and advancing the digital presence of your business.
The important thing to remember, though, is that apps are tools and have to be useful; not just a method for marketing.
If you have a website that encourages interaction, such as a appointment bookings feature, or ordering capabilities, or reservations feature, or online store, etc, then an app is the perfect way to give your customers a great experience on their mobile device.
Similarly, if you have regularly updated content, such as a blog, then an app will be useful for you too.
If your website's sole purpose for being is marketing, and content on the site isn't updated regularly, then an app might not be necessary for you - and it may be difficult for your app to be approved by the app store. You can still create your app and have it listed in the My Mobile App Directory, though.