Why is a program that runs in multiple threads needed instead of one?

Multithreading allows:

1. To increase performance by utilizing multi-core processors. Threads can run in parallel, reducing the overall execution time of a task.
2. To improve the responsiveness of the user interface. Long-running operations are performed in background threads, not blocking the main UI thread.
3. To simplify development for inherently parallel tasks (e.g., processing multiple requests simultaneously).
4. To more efficiently utilize system resources (CPU, GPU).

In a single-threaded application, one long task blocks the execution of everything else. Multithreading allows dividing tasks and executing them independently of each other.