depends on the business, but no not really.
we build mobile apps, and i would say probably half of them aren't necessary. If you have a website that is mobile responsive, there is no need to have an application, that does the same thing
Price will be determined by rather or not it's for android or iOS, and rather it's a native app, two native apps ore one hybrid app, rather ot not what and which framework will be used (ionic or swift etc)
We've built an app for as little as $600. We've built an app for as much as $15,000. it just depends.