Why Requirements and use cases in LLD? - Purpose & Use Cases

The Big Idea

What if you built a system nobody wanted because you skipped this crucial step?

The Scenario

Imagine building a complex system like an online store without writing down what it should do or who will use it. You just start coding based on guesses.

The Problem

This guesswork leads to confusion, missed features, and lots of rework. Developers waste time fixing things that don't meet real needs, and users get frustrated.

The Solution

By clearly defining requirements and use cases upfront, everyone understands what the system must do and how users will interact with it. This guides design and development smoothly.

Before vs After

✗ Before

Start coding without clear goals; fix bugs as they appear.

✓ After

Write requirements and use cases first; build features that fit real needs.

What It Enables

Clear requirements and use cases enable building systems that truly solve problems and delight users.

Real Life Example

Before launching a ride-sharing app, defining use cases like booking rides, driver matching, and payment ensures the app works well for both riders and drivers.

Key Takeaways

Requirements clarify what the system must do.

Use cases describe how users interact with the system.

Together, they prevent costly mistakes and guide effective design.