HI Anon, this is a question that requires a little more infomation to be answered in any helpful manner because it really does depend on your business.  Can you tell us what type of business you have, and what type of app you are considering.  

One factor that you may like to think about is - how much will the app cost you and what you want to achieve by having it.  Is it for making sure people show up on time (an appointmnet setting app)  or is it to buy your products and services from?  Knowing the result you are wanting will help you decide if an app is the best and/or most cost effective way of achieving your goal.

It depends what the service is.

And don't forget that you can create a website that can be used on a mobile device as well. This means you have one thing to maintaine that will work on desktops, tablets and phones - that's what "Responsive" design is all about.

As Lisa said, a little more informtation about your service will help us answer the question for your particular situation.