What is the benefit of using Fragments in Android, rather than Views?

The main reason to use Fragments are for the backstack and lifecycle features. Otherwise, custom views are more light weight and simpler to implement.

At first, I actually tried to build a phone/tablet app using custom views. Everything appeared to work across phones AND tablets, even switching from single panel to split panel. Where I ran into trouble was with the back button and life cycle. Since I was simply updating views manually...there was nothing keeping track of the history of views and their states. Therefore, the back button did not work as expected and it was difficult to recreate even the latest state during life cycle events, such as when rotating the app. To fix that, I had to wrap my custom views in fragments and use the FragmentManager so that the previous states would be saved and recreated.

I realized after answering that I posted to a similar question a year earlier: https://stackoverflow.com/a/11126397/618881

I'd say Fragments are useful in two scenarios: if you split up views on some devices/orientations and show them in two activities and show all the content in one on other devices. That would be a use case if you go on a tablet or maybe even in landscape mode on a phone: e.g. you show the list of items and the details on one screen. on a phone or in portrait mode you just show one part.

Another use case are reusable views. So if you have some views that are visible on different activities and also perform some actions you could put this behaviour into a fragment and then reuse it. Obviously you could probably do that with custom widgets too.

I wouldn't see any reason for using Fragments for every View and I guess it would just be an overhead. I'm only using them in the first use case and I'd say here it is a simplification.

Android introduced fragments in Android 3.0 (API level 11), primarily to support more dynamic and flexible UI designs on large screens, such as tablets. Because a tablet's screen is much larger than that of a handset, there's more room to combine and interchange UI components. Fragments allow such designs without the need for you to manage complex changes to the view hierarchy. By dividing the layout of an activity into fragments, you become able to modify the activity's appearance at runtime and preserve those changes in a back stack that's managed by the activity.

Here you can read more.