But for an actual brand, developer or publisher wondering if they should do an app or a website, I generally answer that the calculation is much simpler and less technical: 

Do people want to put your icon on their home screen? 

Do you have the kind of relationship, and proposition, that people will want to engage with  enough to put your icon on their phone? If the answer to this is ‘yes’, then you should have an app – if only because the app store is the way to do that that people understand, and they’ll look for you in the app store. Once that app is there, you can leverage all the interesting and sophisticated things that you might do with it, or you might manage the flow of information just like your website, but the app has to be there.

If you don’t have that relationship, then all the clever things you can imagine you could do with Apple or Google’s new APIs are irrelevant and your strategy should focus on the web (and social). (By extension, of course, there are some people legitimately wondering if they should have their own website – should a plumber be on the web or in Yelp?)

Apps versus the web — Benedict Evans

For years I’ve been using a more technical, but not too technical answer to this question (e.g., Do the features you want to build require access to the phone’s hardware?). While most clients get this, this question by the author is much more in a marketer’s wheelhouse although I also wonder if every marketer will want to answer yes.