Now, Software systems are very complex and have multiple subsystems. If any of these sub-systems fails. The complete software system could fail. This could be avoided by E2E testing.
End to end testing verifies software system along with its sub-systems. It is conducted out after system and functional testing and ensures maximum risk detection. You should have good knowledge of the complete system and interconnected sub-system.
For better understanding look at Key Benefits of End-to-End Testing.