You’ve probably asked yourself this as soon as you came across Ionic or hybrid mobile apps in general. My personal opinion on this is if you’re creating an app that should also be accessible via the web such as twitter.com, airbnb.com or ebay.com then ionic framework is a great way to go.
Ionic will enable you to develop for iphone, android and mobile web at the same time without worrying too much about porting to different devices.
What is Ionic framework not good for? I believe it is the wrong choice for any kind of performance based apps, video, photo and music editing and/or recording, 3D apps, or games. For games I would highly recommend Unity.
For some examples of Ionic Apps check out the Showcase Page.