Main benefits of Collections Framework in Java are as follows...

Quality : Using Java Collection Framework improves the program quality, since the code is already tested and used by thousands of developers.

Maintenance : Since most of the Java Collections framework code is open source and API documents is widely available, it is easy to maintain the code written with the help of Java Collections framework. One developer can easily pick the code of previous developer.

Speed : Most of programmers report that their development speed increased since they can focus on core logic and use the generic collections provided by Java framework.

Reusability : Java Collections Framework provides common classes and utility methods than can be used with different types of collections. This promotes the reusability of the code. A developer does not have to re-invent the wheel by writing the same method again.