What leads to the need for using fragments in Android applications?

Fragments in Android are used to create a modular and flexible interface. They allow you to break down the UI into independent parts that can be reused in different activities and adapted to various screen sizes (for example, phones and tablets). This is especially important for supporting different device configurations and screen orientations, as well as for dynamically managing the interface without the need to create multiple activities.

Example: on a tablet, you can display a list and details simultaneously in two fragments, while on a phone, you can switch between them using a single activity with different fragments.