I seem to have this conversation often. While meeting with clients and prospects to discuss their websites and general Internet marketing strategies they lean in and say with some degree of certainty, "we also need an app." My response, 9 times out of 10, is "no, you don't."
Utilized primarily for the marketing and promotion of your products or services, an app will not yield a very good return on your investment. An app must be built for multiple platforms (iOS and Droid at the very least), requires developers who are currently very expensive and in demand, and then will require maintenance for bug fixes and operating system changes.
A user not only has to make a conscious effort to find and then install your app, they also have to make a conscious effort to open it. You might be able to lead users to the app store by providing a friendly link on your website but that still requires effort. Most people won't take those steps. I already have too many apps installed by my kids, like Math Puppy, Castle Doombad, and Celebrity Pimple (don't ask). I don't want more apps I don't plan to use frequently. The other issue is that you also probably don't provide enough regular content to hold users interest and keep them coming back for more. If you don't provide the content and it takes extra steps to open the app, it likely ain't gonna work.
With that said, however, there are many occasions where building a custom app could be very beneficial. Here are some examples:
If you do provide a great deal of content through your website (i.e. blogs, news, white papers, etc) then you could benefit from an app. You'll need solid readership for this, though. If you don't already have a core group of followers who read and share your content, then build that first and then reevaluate your need for a custom app later. If you do, apps can be a great tool that your core users will have with them at the tap of a finger. You can push alerts for new posts and events, provide more integrated sharing methods (email, SMS/texting, facebook, LinkedIn, Twitter, etc), and take advantage of some of the other built-in capabilities, like photos, videos, and GPS.
Let's say you're a manufacturing company or a retail operation, your app could allow users to place orders, virtually assemble and preview products, login to their existing accounts, or interact with your company's data in any number of ways. This reason alone is primarily why companies build apps. Integration with existing databases and applications provides a convenient and easy mechanism to conduct business with you and gives you a big advantage over rivals.
There are many considerations when deciding if you need an app but I can narrow it down to two:
If you can't justify an app, perhaps you should convert your site to a responsive/mobile website. This will improve the overall user experience for everyone who reaches you on a handheld device or tablet and is a great way to push off the need (or perceived need) for an app.